Eaxadata and Oracle Database interview question and answer 2026 part2

Question : process running on exadata storage server

An Oracle Exadata storage server (also known as a "cell") runs three primary software processes that work together to manage data, optimize performance, and maintain system health

CELLSRV (Cell Services): This is the core process of the storage server. It handles the majority of the intelligent Exadata features, including:

• Smart Scan: Offloads SQL processing (filtering and column projection) from the database server directly to the storage layer.
• I/O Management: Processes read and write requests and manages I/O Resource Management (IORM) to prioritize workloads.
• Flash Cache: Manages high-speed flash storage to accelerate data access.

MS (Management Server): This process is responsible for the management and monitoring of the storage server. Its primary tasks include

• Interfacing with management tools like the CellCLI command-line utility.
• Generating alerts and monitoring the hardware and software health of the cell.
• Collecting performance metrics.

RS (Restart Server): A "watchdog" process designed to ensure high availability. Its job is to:

• Monitor the other two processes (CELLSRV and MS).
• Automatically restart them if they fail or crash to minimize downtime

process running on exadata compute server

An Exadata compute server runs Oracle Database, Automatic Storage Management (ASM), and critical Exadata-specific daemon processes. To view these running processes, connect to the compute node as the oracle or grid user and use standard OS commands like ps -ef | grep ora_ or crsctl status res -t

1. Database & Grid Infrastructure Processes

These handle memory, disk I/O, and inter-instance communication:

• ora_pmon_[ORACLE_SID]: Process monitor; cleans up failed user processes.
• ora_smon_[ORACLE_SID]: System monitor; performs instance recovery and cleans up temporary space.
• ora_dbw[0-9]_[ORACLE_SID]**: Database writer; writes modified blocks from memory to disk.
• ora_lgwr_[ORACLE_SID]: Log writer; writes redo log entries to disk.
• ora_lms[0-9]_[ORACLE_SID]*: Lock manager service; coordinates cache fusion in Real Application Clusters (RAC)

2. Exadata-Specific Processes

These background processes run on compute nodes specifically to integrate with Exadata and ASM: 

• diskmon.bin / DSKM: Checks the storage network interface, monitors Exadata storage server (cell) liveness, and handles I/O fencing.
• XDMG: Exadata management process; manages communications between the compute server and Exadata Cells.
• XDWK: Exadata background worker process used for offload and disk group tasks

1) in Oracle Exadata, diskmon.bin (Master Disk Monitor) and DSKM (Disk Monitor Slave) are critical background processes that maintain data integrity, propagate database resource plans, and handle storage communications

Key Functions

• I/O Fencing: These processes monitor the health of Exadata storage cells. If a compute node hangs or experiences a split-brain scenario, diskmon.bin and DSKM work with Cluster Synchronization Services (CSS) to fence off the server, blocking any I/O writes to prevent data corruption.
• Cell Liveness & Network Checks: They continuously verify the status and liveliness of the storage network interfaces and Exadata cells.
• DBRM / IORM Propagation: They dynamically broadcast intra-database I/O Resource Manager (IORM) plans from database instances down to the Exadata storage cells

Process Architecture

• diskmon.bin (Master): A node-wide daemon running on the database servers (compute nodes) as part of Oracle Grid Infrastructure. It handles the bulk of the monitoring and communicates with other diskmon daemons in the cluster.
• DSKM (Slave): There is one DSKM slave process for every active Oracle instance (both RDBMS and ASM) running on the compute node. These slaves serve as the direct communication conduit between your database instances and the Master diskmon daemon

2) In Oracle Exadata, XDMG stands for Exadata Automation Manager. It is a critical, multi-threaded background process that runs on database servers to manage and automate background tasks for Exadata storage

Core Functions

• Storage Maintenance & Monitoring: XDMG monitors all configured Oracle Exadata storage servers and handles automated administrative tasks.
• Cell Offload Configuration: It interacts with Exadata storage cells to facilitate automation for storage metrics and health events.
• Collaboration: It coordinates with other Exadata-specific background processes like XDWK (which manages background diagnostic tasks) and DIAG (for core database diagnostics

3) XDWK (Exadata Database Automation Worker) is an essential background process in Oracle Exadata that executes automation and management tasks requested by the XDMG (Exadata Automation Manager) background process. It operates at the database and Oracle ASM instance levels to maintain high availability.

Key Responsibilities

• Disk and Cell Online: When XDMG detects that a previously inaccessible storage cell or disk has returned to service, the XDWK process executes the commands required to bring the Automatic Storage Management (ASM) disks online.
• Automated Recovery: It assists in handling state changes and structural management across Exadata Storage Servers, ensuring storage pools remain synchronized without manual DBA intervention

Question : what will happend if we  appply  patch on Exadata Storage Server (cell) on a Half Rack

Applying a patch to an Exadata Storage Server (Cell) on a Half Rack allows you to update the cell software or firmware with zero downtime if using a rolling patching method. The patching utility sequentially takes each cell offline, updates it, waits for the ASM disks to resync, and then moves to the next cell

Because an Exadata Half Rack typically consists of multiple cells (e.g., 3 to 6 cell nodes depending on the generation and configuration), applying patches has specific effects and requirements

What Happens During the Patching Process?

The patching process utilizes Oracle's patchmgr utility, running a systematic, automated, rolling update across your Exadata storage

Cell Offline Transition: The target cell is gracefully taken offline. The Grid Disks and ASM Disks housed on this cell are spun down.

Software Update: The Exadata System Software (cell) and underlying firmware are upgraded to your target patch version.

Automatic Resync & Rebalance: After applying the patch, the cell is rebooted. Oracle Automatic Storage Management (ASM) will automatically resynchronize mirrored data and rebalance itself before proceeding to the next cell.

No Database Downtime: Provided your storage is configured with Normal or High Redundancy, your data remains fully accessible from surviving, unpatched cells during the sequence

Key Risks & Considerations

• ASM Redundancy Requirement: Rolling cell patching is only recommended if you use High Redundancy for your Automatic Storage Management (ASM) disk groups. High Redundancy ensures that mirrored copies of your data exist on other cells so you do not risk data loss during an active cell outage.
• Time Required: Exadata patching is a thorough process. Applying patches sequentially in a rolling fashion to multiple cells can take several hours (typically 1 to 2 hours per cell server).
• Non-Rolling Option: If you do not have High Redundancy or need the patch to finish quickly, you can apply a non-rolling patch, but this will require downtime for your databases

Key Considerations Before You Patch

• Rolling Constraints: You can only patch one cell at a time. You should never force the patching process to move to a second cell if the first one fails to reboot or resync properly.
• Impact on Flash Cache: After a cell reboots, its Exadata Flash Cache is initially cold. The automated process allows time for the cache to repopulate before proceeding, but users might notice minor, temporary performance variations on queries accessing the affected storage server.
• Verify Redundancy: Confirm your Exadata disk groups use High Redundancy (triple mirroring) or Normal Redundancy (double mirroring) to prevent data unavailability during the rolling maintenance

How to Prepare & Execute Safely

Before starting, always run the Exachk health-check tool to identify any pre-existing issues (such as configuration errors or software mismatches) that could cause a patch failure. The patching itself is orchestrated automatically using the patchmgr utility

Question : what will happened if we apply patch on Exadata Storage Server (cell) on a x8 Quarter Rack

Applying a patch to an Exadata Storage Server (Cell) on an X8 Quarter Rack updates the server's OS, firmware, and Exadata system software. It will proceed in one of two ways: Rolling (zero downtime for databases) or Non-Rolling (requires full cluster downtime)

The exact behavior and process depend on your execution method:

1. Rolling Patching (Recommended)

• What happens: The patchmgr utility patches and reboots one storage cell at a time.
• Database impact: Zero downtime. Oracle Grid Infrastructure automatically takes the ASM disks on that specific cell offline, re-routes I/O to mirrored copies on the other cells, and rebalances data.
• Time to completion: It will take about 1.5 to 2 hours per storage server (with an X8 Quarter Rack typically containing 3 to 4 storage cells, the full process will take several hours)

2. Non-Rolling Patching

• What happens: All storage cells in the rack are patched and rebooted simultaneously.
• Database impact: Full database downtime. All databases, Oracle Clusterware services, and ASM instances must be stopped beforehand.
• Time to completion: Faster overall patching time, but requires a scheduled maintenance window for the total shutdown and restart of the stack

Key Considerations Before You Start

• Cell Space: Ensure your cells have sufficient space (typically at least 3GB free) on the / root partition to download and extract the patch.
• Database Minimal Pack: All storage cell patches must be accompanied by the Exadata "Database Minimal Pack" or "Database Convenience Pack," which must also be applied to all database compute nodes to ensure compatibility.
• Pre-checks: Always run the prerequisite check (-patch_check_prereq) before applying any update to detect potential conflicts or space issues

Question : what will happened if we apply patch on Exadata Storage Server (cell) on a x8 full Rack

Applying a patch to the Exadata Storage Servers (cells) in an X8 Full Rack updates the cell operating system, firmware, and Exadata System Software (Grid Infrastructure). By default, this runs seamlessly in a rolling fashion, meaning your databases and cluster services remain completely online and available

What Happens During the Patching Process

During a rolling patch, the patchmgr utility processes one storage server at a time, performing the following automated sequence:

1. Grid Disks Offlined: All grid disks and ASM disks on the specific cell are gracefully taken offline.
2. Replication/Resync: ASM high redundancy automatically ensures data remains protected by reading from mirrored copies on other cells.
3. Firmware & OS Update: The OS, flash drivers, and firmware (e.g., cell controller, disk controllers) are patched and the server is rebooted.
4. Rebalance: Once rebooted and online, the cell's ASM disks are resynced and rebalanced safely back into the cluster.
5. Iteration: patchmgr verifies data consistency before automatically moving to the next storage server in the rack

Expected System Impact

• Zero Downtime: Client connections to the databases are not dropped. Transactions continue uninterrupted.
• Temporary Performance Dip: Because the storage pool temporarily operates with one less cell, you may experience a slight drop in I/O throughput and performance while disks are being resynced.
• I/O Latency Spikes: You will likely observe brief spikes in I/O latency as ASM relocates extents and rebalances grid disks

Required Actions & Best Practices

• Running exachk: Always execute the Oracle Exachk tool before patching to detect configuration mismatches or pre-existing hardware faults.
• Check Disk Status: Verify that ASM disks are completely resynced before moving to the next server. Do not force an offline operation if disk groups are in a degraded state.
• Review MOS Notes: For exact procedures, syntax for the patchmgr utility, and a list of known issues, refer to Oracle My Support Document 1553537.1
• 
  

Question  : issue while applying patch on Exadata Storage Server (cell) on a x8 full Rack

When an Exadata Storage Server (cell) fails to apply a patch during a rolling patch cycle on an X8 Full Rack, it usually means the patchmgr session was interrupted, an ASM deactivation outcome failed, or the cell services (celld) failed to start after a reboot.

1. Identify the Failure Source

Navigate to the patch manager logs to find the exact root cause of the failure:

• ** patchmgr Log:** /var/log/cellos/patchmgr.log (or .trc for detailed traces)
• Cell Node Log: /var/log/cellos/dbnodeupdate.log

2. Common Causes and Troubleshooting

• ASM Deactivation Outcome Failures: The patch will not proceed if Automatic Storage Management (ASM) disk deactivation fails or times out. Check if the cell disks are safely offline and all grid disks are inactive before running the cell update.
• Storage Server Fails to Boot: If a storage cell hangs during the reboot cycle, verify the ILOM status and check for hardware alerts. You may need to use the shutdown -r now command via the ILOM console to manually restart.
• Active Hardware Alerts: Unresolved alerts (e.g., faulty disks or RoCE network issues) can stop the patching process. Bypass these with the -ignore_alerts flag if you have verified the hardware is safe.
• Disk Repair Time Exceeded: Verify the disk_repair_time setting using cellcli. If it is set too low, the disks might be force-dropped by ASM, causing the patch to halt

3. Review Official Documentation

Review the hardware requirements and system software patches to ensure all prerequisites are met:

• Consult the Oracle Exadata Database Machine Maintenance Guide for exact command usage and maintenance standards.
• Review My Oracle Support Document 1553103.1 for patchmgr usage and resolving dependency or RPM errors.

Question : iorm configuration on a x8 full Rack

Configuring I/O Resource Management (IORM) on an Exadata X8 Full Rack (8 database nodes and 12 storage servers) prevents noisy neighbors and guarantees that critical databases receive necessary I/O bandwidth. Since IORM is cell-based, you must apply the configuration to all 12 storage servers

Key IORM Objectives

Before configuring, choose the optimization objective that best fits your workload

auto: Dynamically adjusts based on workloads; recommended for most environments.

balanced: Balances high throughput and low latency.

low_latency: Best for strict, critical OLTP workloads.

high_throughput: Best for heavy DSS / Data Warehousing workloads

Question : x5 to x10m changes in exadata

The evolution from Exadata X5 to X10M represents a massive architectural leap, transitioning from legacy Intel processors and InfiniBand to 4th-Gen AMD EPYC processors and ultra-fast RDMA over Converged Ethernet (RoCE). This generational shift drastically multiplies compute core counts, flash capacities, and query performance, while heavily increasing data center sustainability

1. Compute & Architecture

• Processors: X5 relied on 18-Core Intel Xeon processors. X10M features massive 96-Core 4th-Gen AMD EPYC processors, providing a massive surge in consolidation density and parallel processing power.
• Storage Offloading: Storage servers now feature their own AMD processors with over 3x the cores of older generations, allowing much heavier, faster Smart Scan SQL query offloading directly on the storage nodes.
• Interconnect Fabric: X5 used InfiniBand, while X10M uses ultra-high-speed RoCE (RDMA over Converged Ethernet) to handle east-west traffic with extreme low latency

2. Memory & Capacity

• Database Servers: RAM capacity has exploded. While X5 maxed out around 768 GB per server, X10M supports much higher capacities, enabling massive memory-intensive in-memory workloads.
• Storage Tiers: In 2023, Oracle replaced legacy Persistent Memory (PMEM) with XRMEM (Exadata RDMA Memory) technology.
• Flash & Disk: High-Capacity (HC) storage servers use significantly larger density HDDs, and Extreme Flash (EF) arrays feature up to 30.72 TB capacity-optimized flash drives, resulting in 2.4x the flash density of prior generation

3. Storage Capacity

• High Capacity (HC) Servers: Shifted from twelve \(8\text{ TB}\) HDDs (\(96\text{ TB}\) raw) in X5 to twelve \(22\text{ TB}\) HDDs (\(264\text{ TB}\) raw).
• Extreme Flash (EF) Servers: Moved from older 1.6TB PCIe cards to immense capacity-optimized \(30.72\text{ TB}\) flash drive

Key Enhancements & Upgrades

Feature / Metric	Exadata X5 Storage Server	Exadata X8M Storage Server	Enhancement
Network Fabric	40 Gb/sec InfiniBand	100 Gb/sec RoCE	Massive increase in bandwidth
I/O Latency	to  $$  (Flash)	(Persistent Memory)	10x lower latency for OLTP
Write Accelerators	Standard Flash Cache	Native PMEM Commit Accelerator	8x faster log writes; commits without OS overhead
Processors	Intel Xeon E5-2699 v3 (Haswell)	16-core Intel Xeon Cascade Lake	Higher core counts for offloading
Storage Architecture	Dual-port PCIe 3.0	RoCE Network Direct Memory Access	Bypasses software & network stack entirely

Question: OCR corruption RAC and fixing issue

Corrupt Oracle Cluster Registry (OCR) in Oracle RAC will crash your clusterware stack. Fortunately, Oracle maintains automatic, daily backups of the OCR. You can restore the latest healthy backup using the ocrconfig utility without reinstalling the software

How to Restore OCR from Backup

Perform these steps with the root user on the primary node

Stop CRS on all nodes:
crsctl stop crs -f

Start CRS in exclusive mode on the local node:
crsctl start crs -excl

List available OCR backups:
ocrconfig -showbackup

Restore the latest OCR backup:
Choose a backup file (e.g., backup00.ocr) from the output and run:
ocrconfig -restore <full_path_to_backup_file>

Stop exclusive CRS mode:
crsctl stop crs -f

Restart CRS normally on all cluster nodes:
crsctl start crs

Verify cluster integrity:
Check the OCR health with:
ocrcheck

Question : if voting disk is  corrupted how to fix it

Voting disk corruption in an Oracle RAC environment means the clusterware can no longer track node availability, leading to immediate node evictions (split-brain prevention) or the crash of the Cluster Synchronization Services Daemon (CSSD). To recover from a complete voting disk loss, you must stop the cluster, start it in exclusive mode, and restore/re-create the disks

Symptoms and Diagnosis

You will generally notice a voting disk failure when nodes start spontaneously rebooting or when the CSSD process goes offline

Alert Logs: Check the Grid Infrastructure alert log (located in $GRID_HOME/log/[hostname]/alert[hostname].log) for CRS-1604 or CRS-1606 errors indicating the voting file is offline or corrupted.

Verify Disks: Run crsctl query css votedisk as the grid user to see which disks are affected or missing

Step-by-Step Recovery (If All Voting Disks are Lost)

If your redundancy is completely breached and you cannot access the voting disks, you must recreate or restore them from the Oracle Cluster Registry (OCR) backup

1. Stop Clusterware on All Nodes
Stop the cluster stack across every node in the cluster to ensure no background processes interfere with the repair

crsctl stop crs -f

2. Start the Cluster in Exclusive Mode
Log into your primary node as the root user and start the High Availability Services (OHAS) and CRS in exclusive mod

crsctl start crs -excl

3. Clear Corrupted Voting Disk Headers
If you are reusing the same LUN or ASM disk group, clear the corrupt headers so the cluster will not attempt to read the old, broken data

For an ASM disk: Recreate the diskgroup or clear the header with dd if=/dev/zero of=[disk_path] bs=1M count=100

4. Replace or Re-add the Voting Disk
Use the crsctl replace votedisk command to point the cluster to a valid ASM disk group or shared storage path. For example, if your voting disk is residing in an ASM diskgroup named +VOTE

crsctl replace votedisk +VOTE

5. Verify and Restart
Check the voting disk configuration to verify that the replacement was successful

crsctl query css votedisk




Once verified, stop CRS on the primary node (so it starts normally), and restart the clusterware on all remaining nodes to rejoin the cluster

Best Practices for Prevention

• Odd Number of Disks: Always use an odd number of voting disks (typically 3 or 5) to ensure quorum and prevent split-brain scenarios.
• Multipathing: Use reliable multipathing (MPIO) to prevent LUN disconnects that simulate disk corruption.
• Hardware Redundancy: Ensure your underlying storage implements mirroring or RAID so that a single disk failure does not surface as a voting disk corruption to the cluster layer

Question : vm cluster network in exacs server

A VM Cluster Network (VCN) in Oracle Exadata Cloud Service (ExaCS) defines the foundational network resources (IP addresses, hostnames, and subnets) allocated to your Exadata VM cluster. It specifically maps out the Client Network (for database and application connections) and the Backup Network (for RMAN and backup operations)

Key Components of an ExaCS Network

• Client Network: The primary interface used by applications and users to connect to the databases (via Oracle RAC) running on the cluster.
• Backup Network: An isolated network used exclusively for transferring large database backups securely.
• Virtual Cloud Network (VCN): You must provision a VCN within your region or virtual environment before building the VM cluster.
• Subnets: The network requires at least two subnets (or distinct VLANs for on-premises Cloud@Customer deployments) to keep the client and backup traffic separated

How to Manage the VM Cluster Network

1. Access the Console: Navigate to the Oracle Exadata Database Service section in your OCI (Oracle Cloud Infrastructure) or cloud console.
2. Define Subnets: Ensure your VCN has the correct routing and DNS resolution rules in place prior to launch.
3. Configure the Network Profile: When creating or managing a VM cluster, you will define the IP address allocation, netmasks, and hostnames for both the Client and Backup networks.
4. Network Security Groups (NSGs): You can assign up to 5 NSGs to both the client and backup networks for strict access control and firewall rule enforcement

Question : what is backup network details in exacc

In Oracle Exadata Cloud@Customer (ExaCC), the backup network is a dedicated private channel separate from the client network. It is used exclusively to route RMAN backups, bulk data transfers, and recovery traffic, preventing large jobs from degrading production performance

Core Architecture & Specifications

• Bonded Interface: Uses the secondary bonded interface (bondeth1) on each database server.
• Physical Connections: Requires dedicated physical uplinks (typically dual 25Gbps or 100Gbps) connecting the compute nodes to your corporate network switches.
• Routing: Traffic is non-routable over the client subnet; it requires specific static routes on compute nodes to force backup traffic onto the bondeth1 interface.
• IP Addressing: Requires a minimum of 1 IP address per node for the backup subnet, plus 3 reserve IP addresses

Network Settings Configuration

When configuring the VM Cluster Network for your ExaCC, you must provide the following: 

• VLAN ID: A virtual LAN identifier (1 to 4094) for VLAN tagging.
• IP Address Range: Starting IP range for the database servers using CIDR notation.
• Netmask & Gateway: Subnet mask and the default gateway for the backup network.
• DNS & NTP: Can be configured to route through this network if localized backup infrastructure (like NFS or ZDLRA) is used

For more Details

https://docs.oracle.com/en/engineered-systems/exadata-cloud-at-customer/ecccm/ecc-manage-vm-cluster-network.html#GUID-B552A943-1F78-4539-B089-DB11EA8565F1

Question : how to convert cdb to pdb

Converting a non-CDB (non-Container Database) to a PDB (Pluggable Database) is a standard database migration process in Oracle 12c and later versions. You perform this by generating an XML metadata file from the non-CDB and then plugging it into the target CDB

To convert your non-CDB into a PDB:

Step 1: Prepare and Describe the Non-CDB

1. Cleanly shut down your non-CDB database and restart it in READ ONLY mode to ensure transactional consistency:

SHUTDOWN IMMEDIATE; 

STARTUP OPEN READ ONLY;

2. Generate the XML description file using the DBMS_PDB.DESCRIBE package:

BEGIN DBMS_PDB.DESCRIBE(pdb_descr_file => '/tmp/noncdb_desc.xml'); END; /

3. Shut down the non-CDB database completely:

SHUTDOWN IMMEDIATE;

Step 2: Plug into the CDB

1. Connect to your target CDB and check if the non-CDB is compatible:
   
   

   SET SERVEROUTPUT ON;
   DECLARE
       l_compatible BOOLEAN;
   BEGIN
       l_compatible := DBMS_PDB.CHECK_PLUG_COMPATIBILITY(
           pdb_descr_file => '/tmp/noncdb_desc.xml');
   END;
   /

Check for any errors by querying PDB_PLUG_IN_VIOLATIONS.

Create the new PDB using the XML file

CREATE PLUGGABLE DATABASE my_new_pdb USING '/tmp/noncdb_desc.xml' COPY FILE_NAME_CONVERT = ('/old_noncdb_dir/', '/new_cdb_dir/my_new_pdb/');

Step 3: Run the Conversion Script

1. Switch to your newly created PDB container

ALTER SESSION SET CONTAINER = my_new_pdb;

Run the non-CDB to PDB script to clean up dictionary entries:

sql

@$ORACLE_HOME/rdbms/admin/noncdb_to_pdb.sql

Open the PDB and save the state so it automatically starts with the CDB:
sql
ALTER PLUGGABLE DATABASE OPEN;
ALTER PLUGGABLE DATABASE SAVE STATE;

For more Details

https://docs.oracle.com/en/database/oracle/oracle-database/18/spucs/create-pdb-using-a-non-cdb.html

https://oracle-base.com/articles/12c/multitenant-migrate-non-cdb-to-pdb-12cr1

Question : how to change  tde encryption to AES256 in oracle

To update or set Oracle Transparent Data Encryption (TDE) to use the AES256 algorithm, you can implement it at the tablespace or column level. If left unspecified, Oracle defaults to AES128

Follow these steps to configure and apply AES256 for your database data

1. Set AES256 as the Default Algorithm (Optional, for 19c and above)

To ensure all newly created tablespaces default to AES256 rather than AES128, run the following as a SYSDBA

ALTER SYSTEM SET "_tablespace_encryption_default_algorithm" = 'AES256' SCOPE = BOTH; ALTER SYSTEM SET ENCRYPT_NEW_TABLESPACES = ALWAYS SCOPE = BOTH;

2. Encrypt a New Tablespace using AES256

When you create a new tablespace, explicitly define the USING 'AES256' clause

CREATE TABLESPACE secure_data DATAFILE '/u01/app/oracle/oradata/db_name/secure_data01.dbf' SIZE 500M ENCRYPTION USING 'AES256' DEFAULT STORAGE(ENCRYPT);

3. Encrypt an Existing Tablespace

Because existing tablespaces cannot be altered to add encryption directly, you must create a new encrypted tablespace (as shown in Step 2) and move the tables over. For example

sql

ALTER TABLESPACE original_tbs OFFLINE NORMAL;

ALTER TABLESPACE original_tbs ENCRYPTION USING 'AES256' ENCRYPT; 
-- Note: This syntax only applies to online tablespace rekeys if your Oracle version supports it. Otherwise, create a new AES256 tablespace and move objects with: 
-- ALTER TABLE my_table MOVE TABLESPACE secure_data;

ALTER TABLESPACE original_tbs ONLINE

4. Encrypt Specific Table Columns using AES256
For column-level TDE, add the USING 'AES256' clause to your table definition or modify an existing column: [1]
sql
-- Create a new table with an encrypted column
CREATE TABLE employees (
    emp_id NUMBER,
    ssn VARCHAR2(11) ENCRYPT USING 'AES256'
);

-- Or rekey an existing encrypted column to AES256
ALTER TABLE employees REKEY USING 'AES256';



What to check next
To confirm the encryption algorithm currently in use for your tablespaces or columns, use Oracle's data dictionary views:
Tablespaces: Query V$ENCRYPTED_TABLESPACES to check ENCRYPTIONALG.
Columns: Query DBA_ENCRYPTED_COLUMNS to verify the ALGORITHM column

For more Details
https://docs.oracle.com/en/database/oracle/oracle-database/12.2/tdpsg/encrypting-data-with-oracle-transparent-data-encryption.html#GUID-3D055E66-51CB-4C5F-880D-66482FF25DF6

Question: How to upgrade from 13c oem

Upgrading from an older Oracle Enterprise Manager (OEM) 13c release to a newer version (such as 13.5) involves a phased system upgrade. The upgrade sequence always goes in this order: Repository Database \(\rightarrow \) Oracle Management Service (OMS) \(\rightarrow \) Management Agents

Step 1: Meet Prerequisites & Verify Patch Paths

1. Check your current version path: Depending on your current version of OEM 13c, you may need an intermediate upgrade.
2. Review System Requirements: Ensure your host operating system, memory, and database versions are certified for the target release. Use the Oracle Certification Matrix to verify requirements.
3. Run Repository Preparation: The underlying Repository Database must be upgraded to a certified version (e.g., 19c or higher) prior to upgrading OMS

Step 2: Upgrade the OMS (Software and Repository)

1. Back Up: Always take a full backup of your current OMS environment and Management Repository before making changes.
2. Download Target Binaries: Download the target version's installation binaries (e.g., em13500_linux64.bin for OEM 13.5) from Oracle Software Delivery Cloud.
3. Run the Installer: Run the installer in GUI or Silent mode.
   • Navigate to the directory with your binaries and launch ./em13500_linux64.bin.
   • Choose the Upgrade option when prompted in the installer wizard.
4. The installer will automatically upgrade the existing OMS and Management Repository schemas

Step 3: Upgrade the Management Agents

Once the central OMS is upgraded, you must update the remote management agents monitoring your targets.

1. Use the Agent Upgrade Console: Log in to the OEM Console, navigate to Setup \(\rightarrow \) Manage Cloud Control \(\rightarrow \) Upgrade Agents.
2. Select the upgradable agents and create an upgrade job.
3. Alternatively, you can use Agent Gold Images to manage and standardize agent updates across your environment

For more Details

Overview of Upgrading to Enterprise Manager Cloud Control 13c

Question : upgrade oms 13.5 to 24ai

To upgrade Oracle Enterprise Manager (OEM) from 13.5 to 24ai, ensure your source is on at least 13.5 RU22 and the repository database is certified (e.g., 19c or higher). Download the 24ai software from Oracle Software Delivery Cloud, run the installer, and select "Upgrade" to perform an out-of-place upgrade. 

Prerequisites and Preparation

• Source Version: You must be on OEM 13.5 Release Update 22 (13.5.0.22) or higher to perform a direct upgrade. If you are on an older version, first apply the required Release Updates to your 13.5 environment.
• Database Requirements: Ensure your Management Repository Database is certified for 24ai (19c+ with minimum Release Updates).
• System Limits: On the OMS host, set the open file limit temporarily for the installation user: ulimit -n 65536.
• Backups: Take a full backup of your existing OMS, Oracle Management Repository (OMR) database, and any associated configurations.
• Plugins: Undeploy any obsolete plugins and download/stage any 24ai-compatible plugins you need to the installation directory

upgrade Steps

1. Download the Software: Go to Oracle Software Delivery Cloud and search for "Enterprise Manager Base Platform – OMS." Download all the necessary ZIP archives for your platform (e.g., Linux x86-64).
2. Extract Files: Extract the downloaded ZIP files to a common staging area (e.g., /u01/install/24.1/Base).
3. Run the Installer: Launch the 24ai installer executable. For a graphical interface, run:
   bash

   ./em24100_linux64.bin
   
   
   

1. Choose Upgrade Option: Select Upgrade End-to-End to upgrade the OMS and the Repository together, or select individual upgrade components depending on your architecture.
2. Run Configuration Scripts: At the end of the installation process, the installer will prompt you to run the root scripts (e.g., allroot.sh) to complete the configuration

Post-Upgrade

• Agents: Starting with 24ai, the central management agent on the OMS host is upgraded by default. For remote targets, you can use the Agent Upgrade Console or create Agent Gold Images to upgrade your remaining fleet to 24ai.
• Patches: Plan to apply the latest Release Updates (RU) to your new OEM 24ai environment to maintain continuous delivery features.

For detailed documentation and the complete certification matrix, refer to the Oracle Enterprise Manager Upgrade Guide. 

For More Details

Overview of Upgrading to Enterprise Manager 24ai Release 1

Question : during pdb startup, its associated service has not started

By default, Oracle Database Container Databases (CDB) do not automatically start their Pluggable Databases (PDBs) or associated custom services upon startup. To resolve this, you must open the PDB and save its current state or explicitly start the custom services using DBMS_SERVICE

Immediate Fix: Open PDB and Services

If your PDB is already open but services are missing, you can force them to start:

• Open with all services: ALTER PLUGGABLE DATABASE <pdb_name> OPEN SERVICES=ALL;
• Manual registration: If services still aren't visible in the listener, run ALTER SYSTEM REGISTER; from within the PDB session

Permanent Solution: Save PDB State 

To ensure the PDB and its services start automatically whenever the CDB starts, you must save the current state after opening it: 

1. Open the PDB: ALTER PLUGGABLE DATABASE <pdb_name> OPEN;
2. Save the state: ALTER PLUGGABLE DATABASE <pdb_name> SAVE STATE;
   • To do this for all PDBs: ALTER PLUGGABLE DATABASE ALL SAVE STATE;
3. Verify: Check the DBA_PDB_SAVED_STATES view to confirm

Troubleshooting Connectivity Issues

If the service is running but you cannot connect:

• Listener Configuration: Ensure the local_listener parameter inside the PDB points to the correct host and port.
• Naming Conflicts: Avoid service names that start with the PDB name followed by a dot (e.g., PDB1.myservice), as this can cause connection errors in versions 18c and 19c.
• Legacy Method: For Oracle 12.1.0.1, which lacks the SAVE STATE command, use an AFTER STARTUP trigger on the database to open all pluggables.

or

1. Enable Automatic PDB Startup (and Default Services)

Starting with Oracle 12c (12.1.0.2), you can configure Oracle to remember and restore the open state of a PDB. The default service for the PDB will start automatically when the PDB opens. 

Step 1: Open the PDB manually using SQL*Plus

ALTER PLUGGABLE DATABASE <pdb_name> OPEN;

Note: If you want all PDBs to start automatically, replace <pdb_name> with ALL.

Step 2: Save the state

ALTER PLUGGABLE DATABASE <pdb_name> SAVE STATE;

When the CDB restarts, Oracle will automatically mount and open the PDB to this saved state, activating its associated services

2. Manually Start Custom/App-Specific Services

If you have created custom services using DBMS_SERVICE, these might not start automatically just by saving the PDB state

Step 1: Connect to the PDB and verify your services

ALTER SESSION SET CONTAINER = <pdb_name>; 

SELECT name, network_name, open_mode FROM dba_services;

Step 2: Start the specific service manually

EXEC DBMS_SERVICE.START_SERVICE('<service_name>');

3. Check and Restart Missing Listeners
If the PDB is open and the services are started, but external connections fail, your listener may not be aware of the dynamic service registration.
Step 1: Force the database to re-register the services with the listener
ALTER SYSTEM REGISTER;
Step 2: Verify listener status from your command line
lsnrctl status

Question : how to migrate from exacc to exacs

Migrating from Exadata Cloud at Customer (ExaCC) to Exadata Cloud Service (ExaCS) involves shifting from a customer-hosted infrastructure model to Oracle’s fully public cloud model. You can achieve this with near-zero downtime using Oracle Zero Downtime Migration (ZDM) or OCI Database Migration Service

Phase 1: Preparation

Before moving any data, you need to set up your destination:

1. Network Configuration: Configure FastConnect or VPN from your local data center to the OCI region hosting your ExaCS environment.
2. Target Provisioning: Provision your target ExaCS VM Cluster and Database Homes, ensuring the Oracle Database versions match or are newer than your ExaCC environment

Phase 2: Choosing a Migration Method

Depending on your downtime tolerance and the volume of data, choose one of the following methods via Oracle Zero Downtime Migration:

• Logical Migration (Data Pump/OCI DMS): Best if you want to selectively migrate PDBs or re-platform to a newer architecture. It’s highly flexible but requires more temporary storage.
• Physical Online Migration (Data Guard): The recommended "lift-and-shift" method. ZDM creates a physical standby of your ExaCC database in ExaCS and syncs it until you are ready for a swift, automated switchover

Phase 3: ZDM Execution

Using ZDM, you can automate the process seamlessly: 

1. Install ZDM on a separate compute node in OCI.
2. Run an evaluation command using zdmcli migrate database with the -evaluate flag to ensure pre-checks pass.
3. Run the migration command with -pauseAfter (if using Data Guard) to manually verify the standby database in ExaCS before committing the cutover

4. Cutover & Validation

• Perform the role switchover using ZDM (or via Data Guard Broker if performing manual setup).
• Run post-migration validation checks and update your DNS routing, application connection strings, and listener services to point to the new ExaCC cluster

For more details

https://docs.oracle.com/en/cloud/cloud-at-customer/exadata-cloud-at-customer/exacc/considerations-migrating-premises-database-dbcs.html

Question : DO WE NEED TO PATCH STORAGE SERVER FIRST IN EXADATA AND WHY 

Oracle highly recommends patching the Exadata Storage Servers (Cells) before patching the Database Servers (Compute Nodes) and Grid Infrastructure.

Why is this the standard order?

• Backward Compatibility: Exadata Storage Server software features and communication protocols are designed to be backward compatible with older Database Node and Grid Infrastructure versions.
• Seamless Upgrades: Updating the storage cells first ensures that when you take down database nodes one by one to patch them, the upgraded storage servers will safely accept connections from the older Grid Infrastructure stack without breaking functionality.
• Feature Synchronization: Exadata features are deeply integrated between the cell software and the database. Upgrading the cells first ensures the entire infrastructure has access to the latest performance, diagnostic, and security capabilities as soon as the compute nodes are updated

Recommended Exadata Patching Sequence:

1. Exadata Storage Servers (Cells): Patched first, typically using the patchmgr utility in a rolling or non-rolling fashion.
2. InfiniBand / RDMA Switches: Patched next to ensure network stability.
3. Database Compute Nodes (Grid Infrastructure & RDBMS): Patched last, often using opatch and dbnodeupdate.sh.

For step-by-step instructions and version prerequisites (like minimum ASM and GI versions for rolling patches), consult the Preparing Exadata Storage Servers for Update guide. If you are managing this on Oracle Cloud, refer to the Patching and Updating an Exadata Cloud Infrastructure documentation

Question : what will you check in AWR if performance issue in exadata

When investigating a performance issue in an Oracle Exadata environment using an AWR report, you must go beyond standard database tuning and focus on Exadata-specific hardware, storage, and software interaction

1. Exadata-Specific Wait Events

In the Top 5 Timed Foreground Events or Wait Event sections, look for these Exadata-specific bottlenecks

cell smart table scan / cell smart index scan: High time here means Smart Scans are active. If high, check if it's due to large data volumes or inefficient execution plans.

cell multiblock physical read: Indicates traditional Exadata I/O waiting.

direct path read / direct path write: Excessive values indicate heavy I/O bypasses the buffer cache (which is standard for Exadata), but can signify inefficient full-table scans.

Reliable Message: Points to communication overhead between the database nodes (compute nodes) and the storage cells

2. Exadata Server Health & Configuration

Always start by confirming the storage environment's state: 

• Exadata Health Report: Scroll to the Exadata section to check for offline disks or open hardware/software alerts.
• Storage Configuration: Ensure all storage cells share the same software release and flash memory configuration. Inconsistent environments commonly cause unpredictable performance
• 3. Exadata Smart Scan & Passthrough
  • Passthrough: If Exadata cannot process predicates (e.g., REGEXP_LIKE or complex CASE statements) on the storage cell, it sends data back to the database compute node. Check the Smart IO section in AWR: a high value in the Passthru column means your Exadata is essentially operating as a standard disk array rather than an engineered system

  4. Smart Flash Cache Performance

  Exadata relies heavily on its flash cache. Inspect the Exadata Smart Flash Cache section for: 

  • Flash Cache Misses: Indicates that required data is not being found in the flash tier. This is usually accompanied by a high percentage of physical I/Os directed to standard hard disks.
  • Write Rejections: Checks if data writes were rejected and redirected to disk, possibly due to a full or improperly configured flash cache

  5. Exadata Smart Flash Log & Redo

  If your bottleneck relates to committing transactions (wait events like log file sync), examine the Exadata Flash Log metrics: 

  • Outliers/Prevented Outliers: A high number of prevented outliers indicates that the slower hard disks were bypassed in favor of the flash log to speed up commit times.
  • High latency on flash log writes indicates underlying hardware wear or cell-level CPU contention

  
  
• 6. I/O Imbalance (Compute Nodes vs. Storage Cells)
  • Cell to DB Node Sent Bytes / Reverse Offload: Indicates if there is reverse offloading occurring. This happens when storage servers are overloaded and the system must send data back to the compute nodes to balance out the CPU usage.
  • Look for an uneven distribution of workload (load imbalance) across different cells or physical disks, which often leads to localized bottlenecks. [1, 2, 3]
  Next Actionable Tool
  If the AWR report directs you to a storage-level I/O or offload issue, follow up with a SQL Monitor Report for the specific, resource-heavy SQL statements. This breaks down exactly which operations occurred on the database node versus the Exadata cell

How will get hardware failure alert in exadata

You can receive Exadata hardware failure alerts through several integrated monitoring methods, depending on how your infrastructure is set up. The four primary ways to get alerts are: 

1. Auto Service Request (ASR)

For hardware failures, Oracle Auto Service Request (ASR) is the most critical tool. When a component fails, ASR automatically creates a Service Request (SR) directly with Oracle Support and notifies your designated administrators, ensuring parts are dispatched quickly. 

2. Email or SNMP Alerts from Storage Cells & Database Servers

Exadata storage servers (cells) and database nodes (compute nodes) can be individually configured to send out email or SNMP trap notifications for alerts.

• Storage Servers: You can use the ALTER CELL command in CellCLI to configure SMTP settings, specify email recipients, and define the notification policy.
• Database Nodes: You can set up email or SNMP alerts natively through the Oracle Integrated Lights Out Manager (ILOM) web interface or CLI. 

3. Oracle Enterprise Manager (OEM)

If you manage your environment with Oracle Enterprise Manager Cloud Control, you can track the entire Exadata Database Machine from a single dashboard. 

• OEM collects hardware and software alerts via SNMP traps and Management Server (MS) notifications.
• You can configure OEM incidents to trigger email notifications, page administrators, or generate tickets in external systems. 

4. Oracle Cloud Infrastructure (OCI) Monitoring

If you are using Exadata Database Service on Dedicated Infrastructure or Cloud@Customer, alerts and events are integrated directly into the OCI Console.

• You can configure OCI Notifications to trigger alerts for critical infrastructure events (like degraded hardware) and route them via email, Slack, or PagerDuty

How to Check Status Manually

If you want to quickly check the current hardware health on your Exadata nodes without waiting for an alert:

• CellCLI: Run LIST ALERTHISTORY on the storage cells to see recent hardware faults or status changes.
• ILOM CLI: Log into the ILOM of a specific compute node or storage cell and run show -d properties /SYS/MB fault_state to check for motherboard or component faults

Question : what is full index scan and fast full index scan

A Full Index Scan reads the entire index from start to finish in sorted order, block by block. A Fast Full Index Scan also reads the entire index, but in no particular order. Instead, it reads the index physically as it sits on the disk using multiblock I/O.

1. Full Index Scan (FIS)

A Full Index Scan traverses the index tree sequentially, reading leaf blocks one by one using linked pointers

Ordering: The data is returned in the sorted order of the index key.

I/O Type: Uses single-block I/O.

Use Case: Primarily used when you need the final result set to be ordered (e.g., fulfilling an ORDER BY clause) or to avoid a separate sorting step in the execution plan.

Downside: Because it reads block-by-block and follows pointers, it can be slow when scanning massive indexes

2. Fast Full Index Scan (FFS)

A Fast Full Index Scan reads the index completely ignoring the logical order of the data. It treats the index as a "skinny" version of the base table.

• Ordering: The data is not sorted.
• I/O Type: Uses multiblock I/O (just like a Full Table Scan), which is much faster for large amounts of data.
• Use Case: Used as an alternative to a Full Table Scan when a query only needs columns that are already present in the index. At least one column in the index must have a NOT NULL constraint.
• Advantage: Unlike a normal full scan, a Fast Full Index Scan can be heavily parallelized

Summary Comparison

Feature	Full Index Scan	Fast Full Index Scan
Data Order	Sorted (in index order)	Unsorted (as stored on disk)
I/O Mechanism	Single-block reads	Multi-block reads
Parallelism	Cannot be parallelized	Can be parallelized
Eliminate Sort	Yes, it can eliminate explicit sorting	No, it does not sort the data
Best Used For	Queries requiring ordered output	Aggregate operations like COUNT(*)

Common Use Example

If you run SELECT COUNT(*) FROM employees;, the database will typically choose a Fast Full Index Scan because it just needs to count the number of entries, not retrieve the data in order. However, if you run SELECT * FROM employees ORDER BY employee_id; and employee_id is indexed, the database will likely choose a Full Index Scan to utilize the pre-sorted structure of the index

what will you check in AWR if performance issue

If an Oracle database is experiencing performance issues, you should analyze the AWR (Automatic Workload Repository) report in a systematic, top-down approach. Avoid reading the report linearly; instead, focus on isolating the bottleneck using a targeted strategy

1. Check the Executive Summary (DB Time vs. Elapsed Time)

At the very top of the report, compare the DB Time to the Elapsed Time

If DB Time is significantly higher than Elapsed Time, it indicates heavy resource contention or a backlog of concurrent session

2. Analyze the "Top 5 Timed Foreground Events"

Scroll down to the Top 5 events section to find the root cause of the waits

I/O Waits (e.g., db file sequential read or db file scattered read): Points to heavy physical reads, inefficient indexes, or a slow storage subsystem.

CPU Waits (e.g., CPU time or resmgr:cpu quantum): Suggests a CPU-bound system where demand exceeds the available cores.

Locking/Concurrency (e.g., enq: TX - row lock contention or library cache lock): Indicates blocking sessions or bad application locking mechanisms

3. Review the Load Profile

The Load Profile details the workload stress levels

• Look at Hard Parses per sec: A high rate (relative to total executions) means the database is spending too much time generating execution plans rather than running queries. It usually signifies a missing bind variable in the application.
• Look at Physical Reads and Redo Size: High physical reads often point to memory (buffer cache) starvation or un-tuned queries

4. Investigate the "SQL Statistics" Section

Find exactly which queries are causing the waits by scrolling to the SQL sections

SQL ordered by Elapsed Time: Identifies the longest-running queries overall.

SQL ordered by CPU Time: Highlights queries that are monopolizing the CPU.

SQL ordered by Physical Reads: Finds the queries overloading your I/O subsystem.

Action: Use the specific SQL ID provided in this list to generate a SQL Health Check Report or explain plan.

5. Compare with a Baseline

If the performance suddenly dropped, you can't rely on just one report

Run an AWR Compare Periods Report (using the awrddrpt.sql script) between a period when the database ran well and the period when it was slow. This allows you to spot exact differences in wait times and execution metrics.

Leverage AWR Explorer in the Oracle Performance Hub to visualize performance trends and detect abnormalities across your snapshot history

Question :what is remote listener in oracle rac

A remote listener in Oracle RAC is a network listener running on a different node than the database instance, primarily responsible for redirecting client connection requests to the least loaded node, with SCAN (Single Client Access Name) listeners acting as the main remote listeners. They enable cross-node load balancing by allowing instances to register their load information with listeners across the cluster, rather than just the local node's listener

Key Aspects of Remote Listeners in RAC:

• Purpose: They provide high availability and load balancing by receiving connections and redirecting them to the best-performing instance in the cluster.
• SCAN Listeners as Remote Listeners: In Oracle 11gR2 and later, the REMOTE_LISTENER parameter is typically set to the SCAN address (e.g., sales-scan.example.com:1521), which resolves to three VIP addresses and enables client requests to be handled by any available SCAN listener.
• Registration: The LREG process (Listener Registration) of each instance registers with both the local listener and all remote SCAN listeners.
• Difference from Local: While a local listener runs on the same node as the instance, a remote listener does not.
• Configuration: The parameter REMOTE_LISTENER defines the network name for these listeners in the tnsnames.ora file

Benefits of Remote Listeners:

• Server-Side Load Balancing: Remote listeners, especially SCAN listeners, understand the current workload of all RAC instances and direct new sessions to the instance with the lowest load.
• Simplified Client Configuration: Clients only need to connect to the SCAN address, allowing the cluster to scale or change without updating client tnsnames.ora files.
• High Availability: If one remote listener fails, other remote listeners (SCAN listeners) can handle the request

Question : how to migrate RAC database from dell storage to ibm storage

The most efficient way to migrate an Oracle RAC database from Dell storage to IBM storage with zero downtime is to use Oracle Automatic Storage Management (ASM) rebalancing. This method allows you to add the new IBM LUNs to your existing ASM disk groups and then drop the old Dell LUNs, letting ASM handle the data movement in the background while the database remains active

Option 1: Zero-Downtime ASM Rebalance (Recommended) []

This method is ideal if both storage arrays can be presented to the RAC nodes simultaneously. 

1. Present IBM LUNs: Map the new IBM LUNs to all RAC nodes and ensure they are visible at the OS level.
2. Prepare Disks: Label the new IBM disks using oracleasm or asmlib if required.
3. Add IBM Disks: Add the new disks to your existing ASM disk groups.
   • Example: ALTER DISKGROUP DATA ADD DISK '/dev/oracleasm/disks/IBM_DISK1' REBALANCE POWER 10;.
4. Monitor Rebalance: Check the progress in V$ASM_OPERATION. Higher power levels speed up migration but consume more I/O.
5. Drop Dell Disks: Once the add-rebalance finishes, drop the old Dell disks.
   • Example: ALTER DISKGROUP DATA DROP DISK 'DELL_DISK_NAME' REBALANCE POWER 10;.
6. Migrate Vote/OCR: If your voting files and OCR are on the old storage, use crsctl and ocrconfig to move them to a new disk group on the IBM storage.

Option 2: RMAN Backup and Restore (Minimal Downtime) 

If you cannot present both storages at once or prefer a "fresh" setup, use Oracle Recovery Manager (RMAN). 

1. Backup: Perform a full RMAN Backup of the source database.
2. Configure Target: Set up new ASM disk groups on the IBM storage.
3. Restore: Restore the control file and datafiles to the new IBM-backed disk groups.
4. Switch & Recover: Use the SWITCH DATABASE TO COPY and RECOVER commands to point the database to the new storage

Key Considerations

• Multipathing: Ensure you update your multipathing configuration (e.g., IBM Subsystem Device Driver) to recognize the new IBM volumes.
• Grid Infrastructure: Remember to migrate the Voting Disks and OCR separately using crsctl replace votedisk and ocrconfig -replace if they reside on the Dell storage.
• Performance: Use Oracle ASM Filter Driver (ASMFD) if moving to modern IBM FlashSystem storage to improve I/O pathing and security

How the Redirection Process Works in  SCAN listener

How the Redirection Process Works

The connection process follows these specific steps:

1. Initial Contact: A client uses the SCAN name to resolve an IP address (usually one of three SCAN VIPs) and sends a connection request to the SCAN listener.
2. Load Assessment: The SCAN listener identifies which database instance offering the requested service is currently the least loaded. It does this using workload registration information provided by the LREG (Listener Registration) process from each instance.
3. Redirection: Instead of connecting the client directly to the database, the SCAN listener sends a "redirect" message back to the client. This message contains the Local Listener's address (using the node’s Virtual IP or VIP) for the chosen node.
4. Final Connection: The client then initiates a new connection directly to the local listener on that specific node. The local listener finally creates the session or connects the client to a dispatcher

Question : how to clone two rac databases on same server

Cloning two Oracle RAC databases onto the same server (cluster) requires distinct naming, careful ASM storage management, and unique listeners to prevent conflicts. 

Here is the approach to clone two RAC databases on one server:

Prerequisites

• Disk Space: Ensure sufficient ASM diskgroup space for both clones, as each will have its own datafiles.
• Unique SID & Database Names: Create distinct $ORACLE_SID (e.g., CLONE1_1, CLONE1_2 and CLONE2_1, CLONE2_2) for each node.
• Unique DB_UNIQUE_NAME: Set a unique db_unique_name for each clone.
• Listener Configuration: Create separate listeners (e.g., LISTENER_CLONE1, LISTENER_CLONE2) to avoid port conflicts

Steps to Clone RAC Databases (RMAN Method)

1. Prepare the Environment:
• Set up environment variables ($ORACLE_HOME, $ORACLE_SID) for the new clones.
• Create pfile/spfile for new databases with adjusted parameters:
  • db_name
  • db_unique_name
  • db_file_name_convert (if using different ASM disk groups).
  • log_file_name_convert
  • cluster_database=true
• Create directories for admin dump and trace files
• Create password files (orapw) on all nodes

Perform RMAN Duplicate:

• Connect RMAN to target (source DB) and auxiliary (clone DB).
• Run the DUPLICATE TARGET DATABASE command.
• Use DB_FILE_NAME_CONVERT to map ASM paths.
• Crucial: Use DB_UNIQUE_NAME for the clone in the script to ensure they are recognized as distinct, especially if cloning from the same source, as shown in this database cloning documentation

Add Instances and Register Service:

• After cloning, run srvctl add database to register the new database, as mentioned in Oracle RAC cloning guidelines.
• Run srvctl add instance for each node.
• Run srvctl modify database to set the db_unique_name.

Configure Local Listeners:

• Set the local_listener parameter in the new SPFILEs to point to the dedicated listeners created for each clone, according to RAC database cloning steps
• Key Considerations
  • ASM Naming Conflict: Do not allow ASM disk groups of the production system to use the same names as the snapshot/clone disk groups, notes IBM documentation.
  • Resource Contention: Two RAC databases on one server will compete for memory and CPU. Ensure adequate resource allocation, as cautioned in Ask TOM.
  • Memory Management: Adjust SGA/PGA sizes to ensure both databases can run concurrently

Question : how to copy spfile from filesystem to asm

To copy an SPFILE from a local file system to Oracle ASM, use the CREATE SPFILE FROM PFILE command in SQL*Plus to create a new spfile in the diskgroup, then update the local init.ora file to point to it. This approach ensures the database registers the new location

Question : how to copy spfile from filesystem to asm

To copy an SPFILE from a local file system to Oracle ASM, use the CREATE SPFILE FROM PFILE command in SQL*Plus to create a new spfile in the diskgroup, then update the local init.ora file to point to it. This approach ensures the database registers the new location.

Step-by-Step Instructions

1. Create the SPFILE in ASM from the PFILE:

SQL> CREATE SPFILE='+DATA' FROM PFILE='/tmp/init.ora';

Identify the new SPFILE path in ASM:
Login to asmcmd and locate the created file to note its exact path.

asmcmd find +DATA spfile*

Example output: +DATA/db/spfile/spfile.921.1133441623

Update the local initialization file:
Modify the $ORACLE_HOME/dbs/init<SID>.ora file on the filesystem to contain only this line, pointing to the new ASM location:

SPFILE='+DATA/db/spfile/spfile.921.1133441623'

Restart the database:

SQL> STARTUP FORCE; 

SQL> SHOW PARAMETER spfile;

Aternative Method (ASMCMD cp)

You can also use the asmcmd cp command to copy the file directly, though the SQL method above is preferred for database instances

asmcmd cp /u01/app/oracle/dbs/spfileORCL.ora +DATA/orcl/spfileORCL.ora

RAC Specific Note

In a RAC environment, you must update the SPFILE location in the OCR using srvctl




srvctl modify database -d <db_name> -p +DATA/db/spfile/spfile.ora

Question : if you have lost all control files and trace file not available

If all control files are lost and no trace file is available, the primary solution is to recreate the control file using the CREATE CONTROLFILE SQL command based on your knowledge of the database structure, or restore it via RMAN if a autobackup exists

Steps to Recreate Control Files (No Trace/Backup):

1. Shutdown Immediate/Abort: Shut down the instance immediately using SHUTDOWN ABORT.
2. Locate All Datafiles & Redo Logs: You must know the full paths of all datafiles and online redo log members.
3. Construct CREATE CONTROLFILE Command: Write a CREATE CONTROLFILE script. You will need to specify:
• DATABASE <name>
• MAXLOGFILES, MAXDATAFILES, etc.
• List all datafiles (using DATAFILE '...' clause).
• List all redo logs (using LOGFILE '...' clause).
4. • Use RESETLOGS because the control file is new.
5. Start and Execute: Start the instance in NOMOUNT state and execute the script.
6. Recover and Open: Perform media recovery and open the database with reset logs:
   RECOVER DATABASE USING BACKUP CONTROLFILE;
ALTER DATABASE OPEN RESETLOGS; 
Alternative RMAN Method:
If you have an RMAN autobackup, you can restore the control file even without a catalog:
STARTUP NOMOUNT;
RESTORE CONTROLFILE FROM AUTOBACKUP;
ALTER DATABASE MOUNT;
RECOVER DATABASE;
ALTER DATABASE OPEN RESETLOGS;

Note: If datafiles exist in the data dictionary but not in the new control file, they will be listed as MISSINGnnnn

Question :how to migrate 200 oracle database from on prem to oci`

Migrating 200 databases requires a structured, fleet-level automation strategy to minimize risk and manual effort. The recommended approach is to use the Oracle Zero Downtime Migration (ZDM) utility, which is specifically designed to automate large-scale migrations to Oracle Cloud Infrastructure (OCI)

1. Choose Your Migration Method

Depending on your business requirements for downtime, select one of the following methods:

• Physical Online Migration: Best for large production databases requiring minimal downtime. It uses Oracle Data Guard to synchronize the on-premise source with a cloud target.
• Logical Online Migration: Ideal for cross-version migrations (e.g., 11g to 19c) or moving to Oracle Autonomous Database. It leverages Oracle GoldenGate for real-time synchronization.
• Physical/Logical Offline: Simpler but requires application downtime. It uses Oracle Recovery Manager (RMAN) or Data Pump to back up and restore data

2. High-Level Migration Workflow

For a fleet of 200 databases, follow this automated sequence:

1. Preparation: Provision a central ZDM Service Host (Linux VM) to orchestrate all migration jobs.
2. Discovery & Assessment: Use the Cloud Premigration Advisor Tool (CPAT) to scan your 200 databases for compatibility issues or metadata conflicts.
3. Fleet Configuration: Create response files for your databases. ZDM can run multiple migration jobs simultaneously, allowing you to migrate databases in waves (e.g., 10–20 at a time).
4. Data Transfer: Establish a secure connection via OCI FastConnect or VPN. For massive data volumes, consider the OCI Data Transfer Appliance to physically ship data to OCI.
5. Execution: Run the migrate database command via ZDM CLI. Use the evaluate flag first to perform a dry run.
6. Switchover: Once the cloud target is synchronized, perform a controlled switchover to the new OCI database

3. Key Strategy Tips for Large Fleets

• Categorization: Group databases by criticality and complexity (e.g., "Tier 1: High Availability" vs "Tier 3: Dev/Test").
• Validation: Use SQL Performance Analyzer (SPA) to compare performance before and after migration to ensure no degradation.
• Monitoring: Use the OCI Database Migration service, a managed GUI based on ZDM, to track the status of all 200 migration jobs from a single console

Question : Prerequisite to migrate 200 oracle database from on prem to oci

Migrating 200 Oracle databases from on-premises to Oracle Cloud Infrastructure (OCI) is a large-scale project requiring structured planning, assessment, and automation, typically using Oracle Zero Downtime Migration (ZDM) or OCI Database Migration Service (DMS)

Here are the essential prerequisites categorized for a successful, large-scale migration:

1. Assessment and Planning (Pre-Migration)

• Database Discovery & Inventory: Catalog all 200+ databases, including version, size, character sets, and OS platforms.
• Cloud Premigration Advisor Tool (CPAT): Run CPAT on all source databases to detect compatibility issues with OCI targets (e.g., Autonomous Database, Base Database Service).
• Migration Strategy Definition: Determine which databases require online (minimal downtime) vs. offline migration based on business criticality.
• Target Sizing: Size the OCI target infrastructure (e.g., Exadata Cloud Service, VM DB Systems) to accommodate consolidated workloads

2. Networking and Security

• Dedicated Connectivity: Set up OCI FastConnect for high-speed, secure data transfer, especially for large databases.
• Network Security: Configure Virtual Cloud Networks (VCNs), subnets, and security lists.
• Firewall Rules: Ensure required ports are open between on-premises and OCI for ZDM/DMS agents, SQL*Net, and Object Storage traffic.
• Identity & Access Management: Create OCI users, groups, and policies with necessary permissions (Manage database-migration, object-storage, vm-db-systems)

3. Source Database Preparation

• Backup Strategy: Perform full RMAN backups. Ensure ARCHIVELOG mode is enabled.
• Database Version: Ensure source databases are on supported versions (typically 11.2.0.4, 12c, 18c, 19c, or 21c).
• TDE Enabled: If migrating to Autonomous Database, Transparent Data Encryption (TDE) should be enabled on the source, or it must be enabled during migration.
• Clean Up: Remove unused schemas and data to reduce transfer size.

4. OCI Target Preparation

• Landing Zone: Set up the OCI Landing Zone to establish foundational compartments, networking, and security.
• Object Storage: Create OCI Object Storage buckets for staging data pump files or RMAN backups.
• Target Instances: Provision the target database instances (e.g., Target Autonomous Database or Base Database Service)

5. Migration Tools and Access

• Zero Downtime Migration (ZDM): For 200 databases, ZDM is highly recommended for automating large-scale migrations.
• SSH Access: Prepare SSH key pairs for connectivity to source and target servers.
• Software Installed: Install ZDM software on a dedicated Linux server on-premises or in OCI.
• API Keys: Configure API keys for OCI API connectivity

For more Details

https://www.oracle.com/technical-resources/articles/cloud/migrate-db-to-cloud-with-datapump.html

https://docs.oracle.com/en/enterprise-manager/cloud-control/enterprise-manager-cloud-control/13.4/emlcm/database-migration-prerequisites.html#GUID-3FB0F7B7-F221-43BE-8D29-E36A18EF45C0

https://docs.oracle.com/en/database/oracle/zero-downtime-migration/21.5/zdmpl/

Question : issue faced in exadata

Common issues faced in Oracle Exadata include Exadata Smart Flash Cache performance degradation, patching failures due to custom dependencies, and workload imbalances across storage cells. Other challenges involve CPU constraints during consolidation and VM cluster scaling failures

Reviewing these challenges can help maintain stability across Exadata database machine and Exadata Cloud at Customer (ExaCC) environments

1. Exadata Smart Flash Cache Bottlenecks

• Issue: Queries suffer from increased read latencies (e.g., cell single block physical read wait events). This happens when queries bypass the Flash Cache and hit the slower hard disks.
• Cause: Suboptimal caching policies, high internal IO load, or out-of-date caching algorithms.
• Resolution: Monitor cache usage using the Exadata Documentation for Monitoring Flash Cache to optimize I/O paths and hit ratios

2. Patching and Upgrade Failures

• Issue: Grid Infrastructure (GI) or DB Node updates hang or fail during the prerequisite or execution phases.
• Cause: Dependency conflicts caused by custom RPM packages, missing space on VM filesystems, or failure to access the object store.
• Resolution: Ensure custom RPMs are removed before patching and refer to the Exadata Cloud at Customer Troubleshooting guide to diagnose specific patch execution errors

3. Workload and Configuration Imbalances

• Issue: Uneven I/O distribution causes specific storage cells to become system-wide bottlenecks (hotspots).
• Cause: Configuration mismatches across cells or disproportionate workloads hitting a single cell.
• Resolution: Use AWR outlier analysis in your Oracle Enterprise Manager or Exadata Management Pack to spot unbalanced devices and align cell configurations

4. CPU Throttling and Scaling Challenges

• Issue: Consolidated databases face CPU starvation, or scaling/adding VMs fails.
• Cause: Resource outliers and "noisy neighbor" effects in a shared infrastructure limit density.
• Resolution: Utilize Exadata Management Pack's CPU Advisors to track and control consolidation density effectively

for more details

Troubleshooting Exadata Cloud Infrastructure Systems

Question: Common daily issue in exadata

Common daily issues and monitoring tasks for Oracle Exadata environments generally focus on performance bottlenecks, storage cell health, and resource contention. Key daily areas for investigation include

1. Common Daily Performance & Operational Issues

• Exadata Smart Scan Bypassing: Queries might bypass Cell Smart Scan, causing increased I/O and performance degradation.
• Storage Cell Bottlenecks: Uneven I/O distribution can create "hotspots" on individual storage cells, slowing down the entire system.
• Quarantine Mechanisms: The Exadata quarantine feature may trigger, preventing affected components from causing system disruption, but forcing operations into a suboptimal mode.
• Capacity Issues: Daily checks often reveal high utilization of flash cache, hard disk capacity, or overall storage.
• Workload Imbalance: Inconsistent configurations across storage cells can lead to performance gaps.

2. Daily Monitoring & Troubleshooting Tasks (Daily Checklist)

• Check Exadata Alerts: Monitor storage server alert.log files and review cellcli -e list alerthistory for critical alerts.
• Verify Storage Cell Health: Check Cell Server (CELLSRV) status and review daily metrics for flash disk/hard disk I/O and throughput.
• Review ExaChk Reports: Running exachk is recommended for daily or periodic assessment of system health.
• Monitor I/O Resource Management (IORM): Analyze if IORM objectives (low_latency, balanced, high_throughput) are met.
• Disk Replacement Verification: Ensure that failed disks are being automatically dropped and that rebalancing is in progress

3. Key Diagnostic Tools

• CellCLI: Used to monitor storage server metrics, CELLSRV processes, and alert history.
• AWR (Automatic Workload Repository): Essential for identifying bottlenecks like excessive cell smart table scan waits.
• Exadata Storage Server Metrics: Used to track CPU, hard/flash disk I/O, and throughput

Question: issue and Monitor I/O Resource Management (IORM)

I/O Resource Management (IORM) in Oracle Exadata ensures fair sharing or prioritization of storage I/O among multiple databases or workloads by managing storage server resources on a per-cell basis, primarily enabled during I/O contention. Management includes defining objectives (Auto, Balanced, Low Latency, High Throughput) and assigning database shares or limits using CellCLI or OCI console

Key Management & Troubleshooting Tasks

• Enabling/Managing IORM: Use ALTER IORMPLAN in CellCLI to set objective and database plans. On Cloud/VM clusters, you can enable IORM via the OCI console by selecting an objective.
• Setting Objectives:
  • Auto: Dynamically adjusts based on workload.
  • Low Latency: Prioritizes OLTP, limiting flash cache impact by large I/Os.
  • High Throughput: Optimized for large sequential DSS workloads.
• Monitoring Metrics: Use AWR reports and V$ views to check DB_IO_WT_SM_RQ (small I/O wait) and DB_IO_WT_LG_RQ (large I/O wait) to detect bottlenecks.

Troubleshooting & Tuning:

• Check Queue Time: If AWR shows high wait times, adjust IORM plan to increase allocations for struggling databases.
• IORM Advisor: Use the Exadata Management Pack's IORM Advisor for visual analysis of flash I/O consumption.
• Persistent Issues: If high priority apps are lagging, use ALTER IORMPLAN to increase shares or set hard limits for lower priority workloads.

for more detail

Understanding I/O Resource Management (IORM)

Question: Exadata Smart Scan Bypassing

Exadata Smart Scan bypassing (often called "passthrough" mode) occurs when the storage tier stops offloading processing and reverts to sending raw data blocks back to the database server. This eliminates the performance benefits of offloading and can flood the storage network with unnecessary data

Common Reasons for Smart Scan Bypassing

A Smart Scan might be bypassed or fall back to traditional block I/O for several technical or environmental reasons: [1]

• Unsupported SQL Operations or Data Types: Smart Scan cannot handle certain objects like clustered tables, reverse key indexes, or out-of-line LOBs (typically > 4 KB). It is also bypassed if a query selects LONG columns or virtual columns.
• Buffered Reads vs. Direct Path Reads: Smart Scan only works with Direct Path Reads (bypassing the buffer cache). If the database optimizer chooses a buffered read (e.g., for a small table or if the object is in the buffer cache), Smart Scan will not trigger.
• Row-Level Issues: The presence of chained or migrated rows often forces the storage tier to return complete blocks to the database server to resolve the row pointers.
• Resource Constraints: If the storage server's CPU utilization becomes too high, it may stop offloading and return normal blocks to maintain overall system stability.
• Data Consistency Requirements: Scenarios involving uncommitted transactions, SELECT ... VERSIONS queries, or delayed block cleanout can prevent offloading
• because the storage cell cannot independently determine the correct version of the data.
• Configuration Settings: Smart Scan will be bypassed if the cell_offload_processing parameter is set to FALSE or if the tablespace is encrypted but CELL_OFFLOAD_DECRYPTION is disabled

How to Detect Bypassing

You can verify if Smart Scan is being bypassed by monitoring specific database metrics:

• Wait Events: Look for cell smart table scan passthru in your session wait events or AWR reports.
• Session Statistics: Compare "cell physical IO-bytes eligible for predicate offload" against "cell physical IO-bytes saved by storage index" and "cell physical IO-bytes returned by smart scan".
• Execution Plans: Ensure the plan shows TABLE ACCESS STORAGE FULL rather than just TABLE ACCESS FULL

Solutions to Force/Restore Smart Scan

• Set Direct Reads: For serial queries, you can try setting _serial_direct_read = ALWAYS to encourage Direct Path Reads.
• Use Parallelism: Parallel queries almost always use Direct Path Reads, making them much more likely to trigger Smart Scan.
• Fix Chained Rows: Reorganize tables with high row migration or chaining to allow the storage cell to process rows locally.
• Check SQL Syntax: Avoid LONG columns and ensure functions used in filters are offloadable to the Exadata Storage Servers

Question. patching issue in exadata

Exadata patching issues often involve failed patchmgr pre-requisites due to hardware alerts, custom RPM dependencies, or dbnodeupdate.sh errors. Common pitfalls include storage cell connectivity issues, hung upgrades requiring ILOM console intervention, or ASM instances failing to start after compute node reboots

Common Exadata Patching Issues & Solutions

• Failed Pre-requisites: Frequently caused by hardware alerts or misconfigurations. Always run exachk before patching and resolve existing alerts.
• Custom RPM Dependencies: dbnodeupdate.sh may fail if custom packages exist. We recommends removing all custom RPMs before upgrading, avoiding the dangerous -modify_at_prereq flag.
• Compute Node Hang/Boot Issue: If a node hangs during patching, a reboot may be needed, often requiring a rescue if the GRUB prompt hangs.
• ASM/Storage Failure: If ASM fails to start after a patch, check for corrupted storage cells or mismatches between storage cell and compute node versions.
• TNS Errors Post-Patching: ORA-12154 can occur after a Fleet Update, requiring verification of network configuration

Best Practices

• Rolling vs. Non-Rolling: Use rolling patches to maintain availability.
• Use Oracle Knowledge Base & Troubleshooting Guide: Always review the latest Known Issues and follow detailed blogs.
• Pre-checks: Utilize patchmgr with the -precheck option to identify issues.
• Out-of-Place Patching: For Cloud@Customer, leverage out-of-place patching for minimal downtime

Question. latest feature in exadata X7–X10M

The Exadata X10M (released 2023) represents a significant generational leap from the X7-X9M series, focusing on extreme consolidation, higher performance, and AI readiness using 4th Gen AMD EPYC processors. It provides up to 3x more cores, 1.5x more memory, and 2.4x higher flash capacity than prior generations

1. Hardware Enhancements (X10M)

• 4th Gen AMD EPYC Processors: Provides significantly higher core counts (96 cores per socket) to enable massive database consolidation on fewer servers.
• PCIe Gen 5 RoCE Networking: Uses dual-port PCIe Gen 5 network interface cards for 2x 100 Gb/sec active-active RoCE network, totaling 200 Gb/sec per server.
• Expanded Memory Capacity: Supports up to 3 TB of DDR5 DRAM per database server, a 50% increase over previous generations.
• Higher Density Storage:
  • High Capacity (HC) Servers: Feature 22 TB hard disk drives (22% increase).
  • Extreme Flash (EF) Servers: Use capacity-optimized 30.72 TB flash drives, increasing raw flash capacity by 2.4x.
• 2U Server Form Factor: New 2U database servers allow better cooling and support for up to 5 client NICs

2. Software Enhancements (System Software 23.1/24ai/25ai)

• Exadata RDMA Memory (XRMEM) Cache: Uses DDR5 DRAM in storage servers to create a shared, ultra-low latency cache, dropping SQL Read latency to less than 17 microseconds.
• AI Vector Search Acceleration (24ai/25ai): Introduces "AI Smart Scan" to offload vector distance computations and Top-K filtering directly to storage servers.
• Exascale Architecture (24ai): A new architecture that decouples storage management from database servers for "thin cloning" of databases and improved storage efficiency.
• Secure RDMA Fabric Isolation: Enables strong isolation for KVM-based virtual machines across the RoCE network.
• Exadata Live Update (24ai): Allows applying OS updates without restarting the database server.
• Smart Scan Enhancements: Improved offloading of columnar compression and decryption/decompression directly to storage, reducing CPU usage on database server

Summary of Advancements (X7 to X10M)

Feature	Exadata X7	Exadata X10M
Processor	Intel Xeon (lower core count)	4th Gen AMD EPYC (96 cores)
Networking	40Gb InfiniBand	100Gb/200Gb RoCE
Storage Type	Flash Cache	XRMEM + Flash + Disk
Disk Capacity	10 TB HDD	22 TB HDD
Read Latency	~250 microseconds	< 17 microseconds

These enhancements result in a much lower Total Cost of Ownership (TCO) compared to older systems, with 5-year TCOs for older X7-2 systems potentially being 72% to 85% higher due to the energy and capacity efficiency of the X10M

For More Details

https://www.oracle.com/a/ocom/docs/engineered-systems/exadata/exadata-x10m-ds.pdf

https://docs.oracle.com/en/engineered-systems/exadata-database-machine/dbmso/exadata-database-machine-x7-new-features.html

Question. How to troubleshoot Exadata Smart Scan Bypassing

Troubleshooting Exadata Smart Scan bypassing involves ensuring Direct Path Reads are used, checking for unsupported SQL/data types, and monitoring wait events. Key actions include verifying that cell_offload_processing is TRUE, the object is not clustered or using unsupported compression, and using EXPLAIN PLAN to confirm TABLE ACCESS STORAGE FULL




Common Reasons for Smart Scan Bypass

• Access Method: Non-direct path reads (e.g., buffered I/O) prevent smart scans.
• Unsupported Objects: Smart scan does not support Index-Organized Tables (IOTs), clusters, or certain LOB configurations.
• Data Issues: Chained rows or specific encryption types can force passthrough mode.
• Parameter Settings: cell_offload_processing set to FALSE or restricted parallel settings.
• Optimization: Missing _serial_direct_read set to ALWAYS for serial queries

Troubleshooting Steps

1. Check Execution Plan: Confirm the plan shows TABLE ACCESS STORAGE FULL and storage() predicates. If it says TABLE ACCESS FULL (without "STORAGE"), smart scan is not happening.
2. Monitor Wait Events: Look for cell smart table scan passthru wait events, which indicate that the cell is reverting to passing raw blocks.
3. Check Table/Index Attributes: Verify if the table is using advanced compression or is an IOT.
4. Verify Parameter Settings:

SHOW PARAMETER cell_offload_processing;

ALTER SESSION SET "_serial_direct_read"=always;

Examine AWR/Statspack: Review "Cell Smart IO" statistics to compare "Passthru" vs. "Smart" scan sessions.

Analyze SQL Constraints: Check if Materialized Views or Transparent Data Encryption (TDE) are hindering offload.

Identify Bottlenecks: Use diagnostics to check for storage cell CPU saturation (100% usage) that forces passthrough                                                                                                              

For more detail -What to Look For When Monitoring Smart I/O

Question: what is difference between exacc and exacs

ExaCS (Exadata Cloud Service) and ExaCC (Exadata Cloud@Customer) both provide Oracle Exadata performance with cloud economics, but differ in location: ExaCS runs in Oracle’s Public Cloud (OCI), while ExaCC runs inside the customer's own data center. ExaCS is best for full cloud adoption, whereas ExaCC is designed for high security, data sovereignty, and strict compliance needs

Key Differences:

• Deployment Location: ExaCS is hosted in Oracle Cloud Infrastructure (OCI) regions. ExaCC hardware is installed physically in the customer’s data center.
• Infrastructure Management: Both are managed by Oracle (hardware and software).
• Best Use Cases:
  • ExaCS: Organizations ready to move all workloads to the public cloud, requiring fast provisioning and scaling.
  • ExaCC: Regulated industries needing data residency, on-premises compliance, or extremely low latency to existing on-prem systems.
• Scaling: ExaCS allows for faster, on-demand scaling compared to the potentially more involved process for ExaCC.
• Network: ExaCS connects via OCI regions, while ExaCC connects to OCI via a Control Plane Server, keeping data behind the customer firewall

Question. what is General issues in Oracle Exadata Cloud@Customer (ExaCC)

General issues in Oracle Exadata Cloud@Customer (ExaCC) often revolve around its hybrid nature—combining on-premises hardware with OCI cloud control plane management. Key issues include patching failures, network connectivity problems between the customer data center and OCI, and database lifecycle management errors

Common Technical Issues in ExaCC

• Patching Failures: Updates to VM operating systems or Grid Infrastructure can hang or fail during node patching, often requiring manual intervention via patchmgr logs on the VMs.
• Networking and Connectivity: Misconfiguration of the OCI Services Network, slow connectivity, or incorrect DNS settings can break communication between the ExaCC infrastructure and OCI control plane.
• Database Lifecycle Issues: PDB creation failures (especially when running in parallel), failure to add VMs to a cluster, or issues during database scaling (CPU scaling fails).
• Backup Failures: Failed backups to OCI Object Storage, typically caused by incorrect database configurations or blocked access to the network.
• Data Guard Issues: Failures to update the nodelist after Data Guard operations, or standbys failing to restart after a switchover

Operational and Management Issues

• Limited Access to Hardware: Users lack direct access to storage servers, Dom0, or InfiniBand switches, relying on Oracle support for these components.
• Monitoring Constraints: The Exadata tab in the Performance Hub offers a limited, read-only view of storage servers.
• Restricted Actions: In some versions, changing default password settings for grid or oracle users is not allowed.
• Wait Events/Performance: Suboptimal query performance where queries bypass Smart Scan, often due to storage cells quarantining disks

Specific Known Issues (As of 2025/2026)

• TDE Key Issues: Potential TDE (Transparent Data Encryption) key replication issues in Data Guard scenarios.
• Dbaastools Conflicts: Upgrading dbaastools before patching can cause incompatibilities with the existing image, leading to APEX/SQL console access issues.
• Storage Scaling: Scaling up data or backup storage may fail if the additional storage is less than 10 GB

For More Details

https://docs.oracle.com/en-us/iaas/exadatacloud/doc/ecs-troubleshooting.html

https://docs.oracle.com/en-us/iaas/exadata/doc/ecc-troubleshooting-systems.html

Question: challenge in configuring ExaCC

Configuring Oracle Exadata Cloud@Customer (ExaCC) presents challenges primarily involving complex network infrastructure, strict OCI prerequisites, and bridging on-premises hardware with cloud control planes. Common hurdles span across networking, DNS/IP allocations, and automated patching or scaling

Common ExaCC Configuration Challenges

• Complex Network Requirements: ExaCC requires multiple segmented networks (Client, Backup, Administration, and RoCE private networks). A frequent challenge is mapping these to the customer's existing data center switches, requiring specific LACP configurations and compatible uplink parameters.
• IP Address and Subnet Exhaustion: OCI services and the local Control Plane Server (CPS) require careful IP allocation. Using improperly sized subnets (e.g., smaller than the recommended /24) often leads to IP exhaustion during scaling and provisioning operations.
• Control Plane Connectivity: The local CPS needs continuous, secure outbound connectivity to OCI management endpoints. Navigating strict on-premises firewall policies, proxy servers, and routing tables to allow this traffic often causes initial deployment delays.
• DNS & Hostname Resolution: Strict forward and reverse DNS resolution is mandatory for provisioning. Misconfigured DNS zones or lack of integration with corporate DNS servers will cause cluster and grid infrastructure setup to fail
• Database Home and Grid Infrastructure Updates: Managing updates via cloud automation requires precise preparation. Not running prechecks or having insufficient free space in the GI Home (/u01) or DB Home (/u02) often causes patching or scaling failures.
• Resource Limits & Quotas: Scaling operations or adding new Virtual Machine (VM) clusters can fail if OCI tenancy limits are not proactively requested or if physical infrastructure limits (such as available cores) are exceeded

For comprehensive troubleshooting steps on resolving CPU scaling, patching, and virtual cluster provisioning failures, you can refer to the official Oracle Exadata Troubleshooting Documentation.

Question How are patching IN EXADATA CC

Patching in Oracle Exadata Cloud@Customer (ExaCC) is divided into two distinct responsibilities: Oracle-managed infrastructure and Customer-managed software. Updates to hardware and hypervisors are handled completely by Oracle, while you maintain full control over patching your Database Homes and Grid Infrastructure

1. Oracle-Managed Components

Oracle manages and performs updates to the underlying physical infrastructure. This includes

• Physical compute nodes (Dom0)
• Exadata Storage Servers (Cells)
• Network fabric switches
• Power distribution units (PDUs) and ILOM interface

How it works: Oracle notifies you in advance via the Cloud Notification Portal. These updates are applied automatically on a rolling basis (one node at a time) to ensure your databases remain continuously available

2. Customer-Managed Components

You are responsible for patching the software layers that live on top of the hardware

Oracle Grid Infrastructure (GI)

Oracle RAC Databases

Compute Node Operating System (DomU

You can perform these updates using either the OCI Console, APIs, or command-line tools

Patching via OCI Console

Using the Oracle Exadata Database Service on Cloud@Customer console is the most streamlined, automated method for updating your environments

Navigate & Select: Go to the OCI console, select Exadata Database Service on Cloud@Customer, and navigate to your VM Clusters or Database Homes.

Precheck: Always run a pre-check first. This verifies that your cluster meets all prerequisites before the actual patching operation begins.

Apply Update: Select the available Release Update (RU) or patch and click Apply.

Options: Choose whether to automatically run datapatch on the databases in your home

Patching via Command Line

For advanced users or scripted operations, you can connect directly to the compute nodes and use native Exadata tools: 

• Grid Infrastructure & DBs: Use the exadbcpatchmulti or dbaascli utilities to apply patches and automate rolling updates across nodes.
• Operating System: Manage compute node OS and image updates using the patchmgr utility

Best Practices

• Pre-checks are mandatory: Never skip the pre-check step, as it prevents unexpected downtime during the patch window.
• Out-of-Place Patching: Whenever possible, use out-of-place patching mechanisms available in Oracle Enterprise Manager (if applicable to your estate), as it significantly reduces the downtime footprint during database and GI updates

Question :what is different between oracle database from19c to 26ai

The transition from Oracle Database 19c to Oracle AI Database 26ai (released early 2026 as the next long-term support release) represents a shift from a traditional, stable, relational database to an AI-native, integrated data platform

The transition from Oracle Database 19c to Oracle AI Database 26ai (released early 2026 as the next long-term support release) represents a shift from a traditional, stable, relational database to an AI-native, integrated data platform

Key Differences: 19c vs. 26ai

Feature Area	Oracle 19c	Oracle 26ai (AI Database)
Primary Goal	Stability & Performance	AI-Native & Automation
AI Integration	Add-on (OML/Spatial)	Native Vector Search (SQL)
Architecture	Non-CDB/CDB Supported	Multitenant (CDB/PDB) Mandatory
Data Types	Relational, JSON, XML	Enhanced JSON/Relational/Graph/Vector
Management	Manual tuning/indexing	AI-driven tuning/Auto-indexing
Security	Standard robust security	Blockchain Tables, Anti-Tamper
Long-Term Support	Ends 2029-2032	New Long-Term Release

Major Changes and Key Takeaways

• Native AI Vector Search: 26ai allows developers to use SQL to perform semantic searches on vector embeddings, integrating AI into existing queries without needing external vector databases.
• Mandatory Multitenant Architecture: While 19c allows traditional "non-CDB" (non-container) databases, 26ai strictly requires the Container Database (CDB) / Pluggable Database (PDB) architecture. Upgrading from 19c non-CDB will force a migration to a PDB.
• The "AI" in 26ai: Features include intelligent, automatic indexing, faster SQL parsing, and enhanced data analysis capabilities.
• Support and Longevity: 19c remains stable, but 26ai is the next major long-term target for organizations seeking the latest features, security updates, and performance optimizations.
• Simplified Upgrades: Oracle provides "AutoUpgrade" utilities and scheduled, low-downtime options to migrate from 19c to 26ai

Question :how to upgrade oracle 19c to 26ai

Upgrading from Oracle 19c to 26ai is supported directly, primarily using the AutoUpgrade utility, which is mandatory for this version transition. Ensure your 19c database is at a high patch level (e.g., Oct 2025/Jan 2026), install 26ai software in a new home, and run AutoUpgrade in deploy mode to handle pre-checks, upgrades, and non-CDB to PDB conversion

Key Considerations and Prerequisites

• Mandatory Multi-tenant: Oracle 26ai only supports multi-tenant architecture. Non-CDB 19c databases will be converted to Pluggable Databases (PDBs) during the upgrade.
• Method: Use AutoUpgrade (JAR file), as traditional methods like DBUA are not supported for this specific upgrade path.
• Backup: Create a full backup or guaranteed restore point before starting.
Grid Infrastructure: Ensure GI is at 26ai or later



Step-by-Step Upgrade Process
1. Prepare the 26ai Home: Install the Oracle 26ai software in a new Oracle Home.
2. Download AutoUpgrade: Use the latest autoupgrade.jar.
3. Create Configuration File (upg.cfg): Define source (19c) and target (26ai) homes, SID, and log directories.




text

global.global_log_dir=/home/oracle/autoupgrade/logs
upg1.source_home=/u01/app/oracle/product/19.0.0/dbhome_1
upg1.target_home=/u01/app/oracle/product/26.0.0/dbhome_1
upg1.sid=ORCL
upg1.target_pdb_name=PDB26AI


4. Run Analyzer Mode: Check for issues before upgrading.
java -jar autoupgrade.jar -config upg.cfg -mode analyze

5. Execute Upgrade (Deploy Mode): Perform the actual upgrade.

java -jar autoupgrade.jar -config upg.cfg -mode deploy



6. Post-Upgrade: Monitor the logs, 
check the version (SELECT * FROM V$VERSION;), 
and update time zones if necessary


For More Details

https://docs.oracle.com/en/database/oracle/oracle-database/26/fppad/upgrading-to-oracle-database.html
https://docs.oracle.com/en-us/iaas/autonomous-database-serverless/doc/upgrade-to-oracle-database-23ai-with-scheduled-upgrade.html

Question :How to upgrade oracle 23ai to 26ai

Upgrading from Oracle 23ai to 26ai is a direct patch-based transition, not a full upgrade, requiring only the application of the October 2025 (or later) Release Update. No application re-certification is needed. The process aligns with patching procedures for on-premises system

Key Upgrade Aspects

• Patching, Not Upgrading: As 26ai is a progression of 23ai, you apply the update as a regular patch.
• Version Compatibility: Direct update is supported from 23ai, as outlined in the Oracle Documentation.
• Architecture: 26ai supports multi-tenant architecture only; non-CDB databases must be converted.

High-Level Steps (On-Premises)

1. Preparation: Download the latest Oracle 26ai Release Update and update the OPlan tool.
2. Pre-checks: Run the AutoUpgrade utility in analyze mode to ensure there are no issues.
3. Perform Update: Execute the AutoUpgrade utility in deploy mode.
4. Post-Update: Ensure that the database time zone and other parameters are updated as required

Question : prerequisite and how to migrate oracle database to oci

Migrating an Oracle database to Oracle Cloud Infrastructure (OCI) involves preparing the source database, setting up network connectivity (VPN/FastConnect), provisioning target OCI DB services, and using tools like Zero-Downtime Migration (ZDM), Data Pump, or GoldenGate for data transfer. Key prerequisites include running the Cloud Premigration Advisor Tool (CPAT), establishing connectivity, and ensuring appropriate user permissions

Prerequisites for Migration

• Target Infrastructure: A provisioned target DB service (e.g., Autonomous Database, Base Database Service).
• Connectivity: Establish VPN or FastConnect for secure communication.
• Tooling: Use of Zero-Downtime Migration (ZDM) (recommended for minimal downtime) or Oracle Data Pump.
• Assessment: Run CPAT to identify compatibility issues.
• Storage: Object Storage in OCI for staging backups.
• Source Preparation: Create a privileged user on the source database

Steps to Migrate Oracle Database to OCI

1. Select Strategy: Choose between online (Minimal/Zero Downtime using GoldenGate) or offline (Data Pump/RMAN) migration.
2. Run Assessment: Use CPAT to test source database against target requirements.
3. Setup Connectivity: Connect on-premise infrastructure to OCI via VPN or FastConnect.
4. Provision Target: Create the target database on OCI, such as Oracle Base Database Service.
5. Execute Migration:
   • Offline: Use RMAN or Data Pump to backup and restore.
   • Online: Use ZDM to configure Data Guard or GoldenGate for synchronization.
6. Switchover: Perform a final data synchronization and point application to the OCI database.
7. Post-Migration: Validate data and perform performance tuning

For More Details

https://www.oracle.com/in/database/cloud-migration/

Question :oracle database 26ai installation in linux server

Installing Oracle Database 26ai on a Linux server (typically Oracle Linux 8 or 9) has become much simpler thanks to the RPM-based installation method. This method automates most of the OS-level tuning and prerequisite checks that used to be manual.

1. Pre-installation Requirements

Before starting, ensure your server meets the following:

• Memory: At least 2 GB RAM (4 GB+ is highly recommended).
• Storage: Minimum 10 GB of free space (the installation uses ~9 GB under /opt).
• Operating System: Oracle Linux 8 or 9 (or RHEL 8/9).
• Root Access: You need sudo or root privileges. 

2. Prepare the Server

The easiest way to configure your system is by using the Oracle AI Database Preinstallation RPM. It automatically creates the oracle user, sets kernel parameters, and installs required libraries.

bash

# For Oracle Linux 9
dnf -y install oracle-ai-database-preinstall-26ai

# For Oracle Linux 8
dnf -y install oracle-ai-database-preinstall-26ai


3. Download and Install the Software
Download the specific 26ai RPM for your Linux version from the official Oracle AI Database Downloads page.
Once downloaded, install the package:

bash

# Replace with the exact filename you downloaded
dnf -y install oracle-ai-database-free-26ai-23.26.0-1.el9.x86_64.rpm



4. Create and Configure the Database 
The RPM installation only puts the software binaries on your disk. To actually create a database instance, you must run the configuration script provided by Oracle. [1, 2]
Run the config script:
bash
/etc/init.d/oracle-free-26ai configure


Set Passwords: You will be prompted to enter a password for the SYS, SYSTEM, and PDBADMIN accounts.

Wait for completion: The script will use the Oracle Database Configuration Assistant (DBCA) to build the database


5. Set Environment Variables
To use tools like sqlplus easily, add the following to your oracle user's .bash_profile
bash
export ORACLE_SID=FREE
export ORACLE_HOME=/opt/oracle/product/26ai/dbhomeFREE
export PATH=$ORACLE_HOME/bin:$PATH

Run . ~/.bash_profile to apply the changes.
6. Verify the Installation
Log in as the oracle user and connect to the database:

sqlplus / as sysdba




For More Details

https://docs.oracle.com/en/database/oracle/oracle-database/26/xeinl/index.html
https://www.oracle.com/in/database/free/get-started/

Question : two node grid upgradation from oracle database 19c to 26 ai in linux server

Upgrading a two-node Oracle Grid Infrastructure from 19c to 26ai 
(the latest long-term release that replaced the 23ai branding for on-premises) 
is a multi-step process that requires careful preparation, 
as the 26ai version enforces a container-only (CDB) architecture and higher OS requirement

1. Critical Prerequisites
Before starting, ensure your environment meets these standards:
Operating System: Oracle 26ai requires Oracle Linux 8.8+ or Red Hat Enterprise Linux 8.8+. If you are on OL7, you must upgrade the OS first.
Grid Infrastructure First: You must upgrade the Clusterware (Grid Infrastructure) to 26ai before you can upgrade the databases to 26ai.
Direct Path: A direct upgrade from 19c or 21c to 26ai is supported. There is no need to install 23ai as an intermediate step.
ASM Compatibility: Note that starting with 23ai/26ai, Oracle ASMFD (Filter Driver) is desupported. Ensure your ASM devices are managed via standard methods like udev or multipath.
2. Pre-Upgrade Preparation
Download Software: Obtain the 26ai Grid Infrastructure "Gold Image" from My Oracle Support (MOS) or the Oracle Software Delivery Cloud.
Run CVU Pre-check: Execute the Cluster Verification Utility (CVU) to identify potential blockers.

./runcluvfy.sh stage -pre crsinst -upgrade -rolling -srcoh <19c_GRID_HOME> -destoh <26ai_GRID_HOME> -destversion 23.26.0


3. Upgrade Procedure (Rolling Method)
The rolling upgrade allows you to keep the cluster services running on one node while the other is being upgraded. [1, 2, 3]
Prepare the New Home: Create a new directory for the 26ai Grid Home on both nodes and unzip the 26ai software into it.
Launch the Installer: Log in as the grid user on Node 1 and run the setup script:

./gridSetup.sh


Select Upgrade: Choose the "Upgrade Oracle Grid Infrastructure" option.
Execute Scripts: The installer will prompt you to run rootupgrade.sh as the root user.
Node 1: Run /u01/app/26ai/grid/rootupgrade.sh first.
Node 2: Once Node 1 finishes, run the script on Node 2.
Finalize: After both nodes are upgraded, the installer will finish the configuration.

4. Post-Upgrade: Database Upgrade [1]
Once the Grid Infrastructure is running 26ai, you can move your databases from 19c to 26ai. [1]
Use AutoUpgrade: This is the recommended tool. It automates the pre-checks, the upgrade, and the mandatory conversion from Non-CDB to PDB.
Verification: You can use the Oracle AutoUpgrade Tool documentation to download the latest .jar file and generate your configuration file. 

Feature [1, 2, 3, 4, 5]
19c
26ai
Architecture
Non-CDB or CDB
CDB Only
AI Features
Limited
Native AI Vector Search
Linux Version
OL7 / OL8 / OL9
OL8 / OL9 Required
Support
Long-Term
Long-Term (Premier until 2031)







Question : how to migrate oracle database ZDM to OCI

Migrating an Oracle database to Oracle Cloud Infrastructure (OCI) using Zero Downtime Migration (ZDM) involves installing the ZDM software on a separate Linux node, preparing a response file, and executing the migration via CLI. ZDM supports physical (Data Guard) or 
logical (GoldenGate) online/offline migrations to OCI database services with minimal downtime

Key Steps for ZDM Migration:
Prerequisites: Install ZDM on a Linux host (not on source/target) with at least 100GB free space. Ensure connectivity via VPN/FastConnect.
Response File: Define source database details, target OCI database details, and backup locations (Object Storage).
Prepare Target: Create a target database (e.g., Base Database Service).
Execution: Run zdmcli to start the migration, which handles backup, transfer, synchronization, and final switchover


Migration Approaches:
Online Physical (DGoss): Uses Data Guard to create a physical standby, enabling near-zero downtime switchover.
Online Logical: Uses Oracle GoldenGate for ongoing synchronization, useful for cross-version or non-CDB to PDB migration

For More Details

https://docs.oracle.com/en/solutions/migrate-database-with-zdm/index.html

Q. Ensure oracle database security, compliance, and access control management in on-promise

Securing on-premise Oracle Databases involves enforcing the principle of least privilege, 
encrypting sensitive data, and maintaining strict access control. 
Key measures include using Oracle Advanced Security for encryption 
at rest, implementing role-based access control,
q12patching with Oracle Enterprise Manager, and locking default accounts

Core Oracle Security & Compliance Strategies (On-Premise)


Access Control Management:
Least Privilege: Ensure users and roles are granted only the minimum necessary privileges to perform their jobs.
Role-Based Access: Grant privileges to roles, not directly to individual users, to simplify management.
Default Account Management: Lock and expire predefined user accounts immediately, such as SYS and SYSTEM.
Secure Application Roles: Use PL/SQL packages to control when roles are enabled, limiting access by application context.

Data Security (At Rest & In Transit):
Transparent Data Encryption (TDE): Utilize TDE to encrypt sensitive data, which prevents unauthorized access to data stored in data blocks and operating system files.
Data Masking: Apply dynamic data masking to obscure sensitive data during queries, protecting data privacy.
Key Management: Implement Oracle Key Vault to manage encryption keys and secrets efficiently

Compliance & Audit Management:
Audit Privileges: Monitor and audit the use of powerful privileges (e.g., SYSDBA).
Database Auditing: Review DBA_* data dictionary views to track user activity.
Regulatory Compliance: Ensure compliance with data protection policies by ensuring that encrypted data does not linger in files

Infrastructure Protection (On-Premise Specific):
Patch Management: Use Oracle Enterprise Manager Fleet Maintenance to regularly apply quarterly security patches and monthly updates to your database servers.
Operating System Security: Limit operating system user access and restrict access to the Oracle home directory.
Network Security: Ensure the server host is secure and use network-level controls to prevent unauthorized access.
Secure Backup: Encrypt all backup media to secure data

Key Oracle Products for On-Premise Security:
Oracle Advanced Security: Provides TDE and data masking.
Oracle Key Vault: Manages encryption keys.
Oracle Enterprise Manager: For patching and security compliance orchestration.

Question :How to migrate and upgrade Oracle database

Proven experience in Oracle database migrations and version upgrades (e.g., to 19c or 23ai) 
involves utilizing tools like AutoUpgrade for automation and Zero Downtime Migration (ZDM) 
for minimal disruption. Experts handle complex cross-platform migrations, performance tuning, 
and pre/post-upgrade validations to ensure data integrity and 100% availability


Core Competencies & Proven Approaches
Version Upgrades (19c/23ai): Utilizing Oracle AutoUpgrade to automate pre-checks, 
fix issues, and perform upgrades with reduced manual effort.
Migration Strategies: Implementing Cold, Hot, or Refreshable cloning via Oracle ZDM 26.1, 
tailored to downtime tolerance (e.g., minimal-disruption for production).
Cloud Migration (OCI): Moving on-premise workloads to Oracle Cloud Infrastructure (OCI) 
using OCI Database Migration and Data Transfer services.
Minimal Downtime Techniques: Employing physical online migration techniques to keep databases active 
during migration or upgrade.
Validation & Testing: Performing rigorous pre-upgrade analysis and post-upgrade validation 
to ensure application compatibility and performance, 
particularly for complex ERP environments
Tools & Technologies
Oracle ZDM (Zero Downtime Migration)/DMS: For migrating to cloud or on-prem with 
minimal downtime.
AutoUpgrade Utility: Oracle-recommended tool for 19c/21c upgrades.
Data Pump / RMAN: Standard tools for migration and backup/recovery.
OCI Migration Hub: For cloud adoption and migration

Key Focus Areas
Reducing Downtime: Ensuring 100% system availability, or as close to it as possible, 
for critical databases.
Data Integrity: Moving years of business data safely from older versions to 
modernized environments.
Performance Optimization: Tuning new database instances to ensure improved 
scalability and performance

Question :how will do risk assessment for oracle database

To perform a risk assessment for an Oracle database, 
you can use specialized tools provided by Oracle that automate the discovery of security gaps 
and sensitive data.


Primary Assessment Tools
Oracle Database Security Assessment Tool (DBSAT): A free, lightweight command-line utility for evaluating 
on-premises and cloud databases.
Collector: Gathers configuration data and system metadata.
Reporter: Analyzes the collected data and generates a detailed report with prioritized remediation recommendations.
Discoverer: Scans the database to locate and classify sensitive data.
Oracle Data Safe: A unified cloud service for fleet-wide assessments. It allows you to schedule periodic scans, establish security baselines, and monitor "configuration drift" over time

Key Assessment Areas
Your assessment should cover these critical domains to identify potential risks: 
Database Configuration: Review initialization parameters, listener settings, 
and default security policies.
User Security: Identify highly privileged users, excessive entitlements, and 
insecure password policies (e.g., expired or default passwords).
Access Controls: Evaluate existing roles, system privileges, and fine-grained access
 controls to ensure the principle of least privilege.
Auditing and Monitoring: Verify that database auditing is enabled to track sensitive data
 access and privileged user activities.
Data Protection: Check for the use of encryption (like Transparent Data Encryption) 
and ensure that sensitive data is properly identified
General Best Practices
Establish a Baseline: Use DBSAT to create an initial security posture record and compare future assessments against it to spot unauthorized changes.
Regular Patching: Ensure the database is up-to-date by applying the latest Oracle Critical Patch Updates (CPU) on a quarterly schedule.
Compliance Alignment: Map findings against industry standards such as CIS Benchmarks or DISA STIGs to meet regulatory requirements like GDPR. 

Question : how to load good execution plan in oracle hash value

To  Verify performance  issue on database

select sid,serial#,inst_id,sql_id,event from gV$session where sql_id='&sql_id';
select sql_text,sql_id,execution,sql_profile from v$sql where sql_id='&sql_id';
select sql_id,plan_hash_value,executions from gv$sql where sql_id='&SQL_ID';
select sql_id, address, hash_value, plan_hash_value from v$sqlarea wheresql_id='&SQL_ID';



select sql_id,LAST_ACTIVE_TIME,PLAN_HASH_VALUE,ROWS_PROCESSED,EXECUTIONS,END_OF_FETCH_COUNT,LOADS,ELAPSED_TIME/power(10,6)/60,SORTS, PX_SERVERS_EXECUTIONS
from V$SQLSTATS where sql_id='&SQLID';


verify execution explain plan

sql select * from table ( dbms_xplan.display_cursor('&sql_id'))
sql select * from table ( dbms_xplan.display_awr('&sql_id'))


verify execution plan history using below query

col begin_interval_time for a30
break on plan_hash_value on startup_time skip 1
select ss.snap_id, ss.instance_number node, begin_interval_time, s.sql_id, s.plan_hash_value,
nvl(executions_delta,0) execs,
(elapsed_time_delta/decode(nvl(executions_delta,0),0,1,executions_delta))/1000000 avg_etime,
(buffer_gets_delta/decode(nvl(buffer_gets_delta,0),0,1,executions_delta)) avg_lio, version_count 
from DBA_HIST_SQLSTAT S, DBA_HIST_SNAPSHOT SS 
where s.sql_id = nvl('&sql_id','4dqs2k5tynk61')
and ss.snap_id = S.snap_id 
and ss.instance_number = S.instance_number
and executions_delta > 0 --and plan_hash_value=3099046451
order by 1, 2, 3


1. Identify When the Plan Flipped
Join with DBA_HIST_SQLSTAT to find when the PLAN_HASH_VALUE changed for a specific SQL_ID

Check BEGIN_INTERVAL_TIME: Look for the exact snapshot interval where the PLAN_HASH_VALUE changed from a known "good" hash to a "bad" one.
Compare Performance Metrics: Look at ELAPSED_TIME_DELTA, CPU_TIME_DELTA, and BUFFER_GETS_DELTA before and after the flip to confirm the impac

Check for Statistics Updates
Identify if a statistics gathering job ran just before the bad plan appeared.
Check if LAST_ANALYZED dates for involved tables or indexes in DBA_TAB_STATISTICS or DBA_IND_STATISTICS align with the END_INTERVAL_TIME of the snapshot.
Outdated or skewed statistics are a common reason for the optimizer to miscalculate costs

Review Metadata and Object Changes
Index Changes: Use DBA_HIST_SQL_PLAN to check if the new plan is missing an index that was used in the old plan, which might indicate the index was dropped or became unusable.
Bind Variable Peeking: If bind variables are used, check DBA_HIST_SQL_BIND_METADATA to see if a "non-representative" bind value was peeked during the hard parse in that snapshot, leading to a suboptimal plan for other values


Verify Table and Column Statistics
To confirm if outdated or skewed stats are the root cause, check the state of the statistics 
for the tables/indexes involved in the query

Query the DBA_TAB_COL_STATISTICS or DBA_TAB_STATISTICS to check the LAST_ANALYZED date and row counts.
Data Skew & Histograms: Look at the HISTOGRAM column. A high skew in data (e.g., \(99\%\) of values belonging to one category) requires a frequency or height-balanced histogram to prevent the optimizer from assuming an even distribution


Evaluate Schema Object Definitions
Changes in the schema structure itself invalidate old statistics and plans. 
Check if indexes have degraded over time. High values in the BLEVEL (B-Tree Level) column in DBA_INDEXES can cause the optimizer to inaccurately cost index range scans




To load a "good" execution plan in Oracle using its Plan Hash Value (PHV), 
you typically use SQL Plan Management (SPM) to create a SQL Plan Baseline. 
This forces the optimizer to use that specific, high-performing plan even 
if database statistics change later

Loading a Plan from the Cursor Cache
If the "good" plan is currently in the database's shared memory (cursor cache), 
use the DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE function. 
Identify the SQL_ID and Plan Hash Value
Query V$SQL to find the identifiers for your target statement:
SELECT sql_id, plan_hash_value, elapsed_time/executions/1000000 AS avg_sec
FROM v$sql
WHERE sql_text LIKE '%your_query_fragment%';


Load the Baseline
Run the following PL/SQL block, replacing the placeholders 
with your identified values:

DECLARE
  l_plans_loaded PLS_INTEGER;
BEGIN
  l_plans_loaded := DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE(
    sql_id          => 'your_sql_id',
    plan_hash_value => your_plan_hash_value
  );
END;
/



Loading a Plan from AWR (History)
If the "good" plan is no longer in memory but exists in the Automatic Workload Repository (AWR), 
use DBMS_SPM.LOAD_PLANS_FROM_AWR

DECLARE
  l_plans_loaded PLS_INTEGER;
BEGIN
  l_plans_loaded := DBMS_SPM.LOAD_PLANS_FROM_AWR(
    sql_id          => 'your_sql_id',
    plan_hash_value => your_plan_hash_value
  );
END;
/

Verification
After loading, verify that the baseline is Enabled and Accepted in
 the DBA_SQL_PLAN_BASELINES view

SELECT sql_handle, plan_name, enabled, accepted, fixed
FROM dba_sql_plan_baselines
WHERE sql_text LIKE '%your_query%';
or
Quick Summary
The process involves identifying the SQL_ID and the "good" PHV, 
running the script to generate a Profile, and then executing 
that Profile to force the optimizer to use the desired plan. 
Step-by-Step Instructions
Identify SQL_ID and Good PHV
Find the SQL_ID for your query and the specific PLAN_HASH_VALUE t
hat performed well using the V$SQL or DBA_HIST_SQLSTAT views.
\
To load a high-performing execution plan in Oracle using a SQL Profile 
and a specific Plan Hash Value (PHV), 
the most common and reliable method is using the coe_xfr_sql_profile.sql script

SELECT sql_id, plan_hash_value, executions, elapsed_time/1000000 avg_sec 
FROM v$sql WHERE sql_id = 'your_sql_id';

Run the coe_xfr_sql_profile.sql Script

This script is part of the SQLT (SQLTXPLAIN) utility from Oracle Support. 
Run it in SQL*Plus as a user with DBA privileges.
Syntax: @coe_xfr_sql_profile.sql [SQL_ID] [PHV]
The script will prompt you for the SQL_ID and the "good" PLAN_HASH_VALUE.
Execute the Generated Script

The previous step creates a new SQL script in your current directory with a name 
like coe_xfr_sql_profile_[SQL_ID]_[PHV].sql. Run this new script to actually 
create the SQL Profile in the database
.
Syntax: @coe_xfr_sql_profile_gpm6wzuy8yabq_1950795681.sql
Verify the Profile Application

Run your query again and check the "Note" section of the Execution Plan to ensure
 the profile is being used.

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR('your_sql_id', NULL));
Key Considerations
Force Matching: You can modify the generated script to set force_match => TRUE if you want the profile to apply to similar queries that use different literals but the same structure.
Licensing: Using SQL Profiles requires the Oracle Tuning Pack license.
Alternative: For more permanent stability, many DBAs prefer SQL Plan Baselines using DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE because they are easier to manage and evolve

Question : what is different DBMS_SPM between sql profile coe_xfr_sql_profile.sql
and advantage

In Oracle database performance tuning, DBMS_SPM (SQL Plan Management) and the coe_xfr_sql_profile.sql script are both used to stabilize execution plans, 
but they differ significantly in their approach and long-term management.

Key Differences
Mechanism:
DBMS_SPM creates SQL Plan Baselines, which are a set of "accepted" plans that the optimizer is allowed to use. It is proactive and designed for long-term plan stability.
coe_xfr_sql_profile.sql (part of the SQLT toolkit) creates a manual SQL Profile by extracting "outline" hints from a known good plan 
(from the cursor cache or AWR) and applying them to a SQL statement.
Enforcement:
Baselines act as a filter; the optimizer may find new plans, but it can only use them if they are verified and accepted into the baseline.
SQL Profiles (via COE) are often reactive and used to "force" a specific plan by feeding the optimizer specialized hints.
Force Matching:
SQL Profiles have a major advantage in force matching, allowing a single profile to apply to similar SQL statements that differ only in literal values (where bind variables are not used).
Baselines generally do not support force matching in the same way

Comparison Table
Feature 
DBMS_SPM (Baselines)
COE Script (SQL Profile)
Strategy
Proactive (Plan Stability)
Reactive (Emergency Fix)
Control
Constrains optimizer to accepted plans
Pushes optimizer toward a specific plan
Evolution
Automatic or manual verification of new plans
No native evolution; manual update required
Force Matching
No
Yes (handles literals)
Reporting
Alerts if a plan cannot be reproduced
Silent failure if hints no longer apply


Advantages
Advantages of DBMS_SPM:
Self-Learning: It can automatically discover and test better plans in the background (Evolution).
Dependability: It is the most reliable method for long-term enforcement in critical workloads.
Integrity: If the baseline plan becomes unavailable, the database will report it, whereas a profile may silently fail and result in a suboptimal plan.
Advantages of coe_xfr_sql_profile.sql:
Ease of Use: Quickly "pins" a specific known-good execution plan from the past to fix a current performance regression.
Literal Handling: Ideal for applications that do not use bind variables, as it can match SQL statements with different literals.

Portability: The script generates a standalone .sql file that can be easily moved and executed on other environments like UAT or Production.

For more details

https://blogs.oracle.com/optimizer/what-is-the-difference-between-sql-profiles-and-sql-plan-baselines