Oracle RAC DBA Interview Questions
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What is Oracle RAC?
Oracle RAC (Real Application Clusters) is a database clustering solution that allows multiple instances to access a single database simultaneously, providing high availability, scalability, and load balancing.
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What are the key benefits of using Oracle RAC?
High Availability: Ensures database availability in case of node failures.
Scalability: Allows adding more nodes to handle increased workload.
Load Balancing: Distributes user connections across multiple nodes for better performance.
Failover Support: In case one node fails, the workload is transferred to another node. -
What are the components of an Oracle RAC architecture?
Cluster Nodes: Physical or virtual servers running Oracle RAC instances.
Shared Storage: Storage that all RAC nodes access (e.g., ASM, SAN, NAS).
Oracle Clusterware: Manages cluster resources and node communication.
Private Interconnect: High-speed network for RAC instances to communicate.
Voting Disk: Stores information about node membership in the cluster.
OCR (Oracle Cluster Registry): Stores cluster configuration details. -
What is Oracle Clusterware?
Oracle Clusterware is Oracle’s cluster management software that coordinates RAC instances, provides high availability, and ensures communication between nodes.
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If I have a 8-node RAC, then how many scan listeners are required?
For an 8-node Real Application Clusters (RAC), you typically need three Scan Listeners.It is not mandatory for scan listener to run on all the nodes.
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What is the role of SCAN (Single Client Access Name) in RAC?
SCAN provides a single access point for client connections to the RAC database, simplifying connection management and load balancing.
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What is the importance of a Private Interconnect in RAC?
The private interconnect is used for internode communication, cache fusion, and data synchronization. A high-speed, low-latency network is required to prevent performance bottlenecks.
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How SCAN knows which node has least load?
The SCAN (Single Client Access Name) does not inherently know the load on individual nodes. Load balancing is typically managed by the underlying clusterware or load balancing algorithms, which distribute client connections across the nodes in a balanced manner.
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What is Cache Fusion in Oracle RAC?
Cache Fusion is Oracle RAC’s mechanism to share data between instances via private interconnect, ensuring consistency across nodes without disk I/O.
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What is the function of Voting Disk in Oracle RAC?
The Voting Disk helps in cluster membership decisions, ensuring that only the healthy nodes remain in the cluster and avoiding split-brain scenarios.
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Explain how client connection is established in RAC database ?
LREG process on each instances registers the database service of the node with default local listener and scan listener. The listeners store the workload information of each node.
So when client tries to connect using scan_name and port,
1.scan_name will be resolved through DNS , which will redirect to 1st scan ip ( out of 3).
2.The client will connected to the respective scan listener.
3.The scan listener compares the work load of both the instances and if scan determines that node1 has least load , then scan listener send the vip
4.address and port details of that particular nodes local listener to client.Address and port details of that particular nodes local listener to client.
5.Now client connects to that local listeners and a dedicated server process is created.
6.Client connection becomes successful and it starts accessing the database. -
What current block and CR block and PI in RAC?
In Oracle RAC (Real Application Clusters), these terms refer to cache fusion mechanisms:
- Current Block: The most recent copy of a data block, which can be modified by an instance.
- CR (Consistent Read) Block: A past version of a data block used for read consistency, typically reconstructed using undo.
- PI (Past Image) Block: A block retained in an instance’s buffer cache before transferring a modified version to another instance to ensure data consistency.
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What happens if a node fails in an Oracle RAC environment?
The failed node is evicted from the cluster.
Oracle Clusterware redistributes connections to other available nodes.
Instance recovery is performed by the surviving nodes. -
How many instances can one rack database have?
One rack database can have up to 100 instances.
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How does Load Balancing work in Oracle RAC?
Oracle RAC provides two types of load balancing:
Client-side Load Balancing: Clients distribute connections across nodes based on SCAN.
Server-side Load Balancing: The database directs connections based on workload and performance metrics. -
What is Transparent Application Failover (TAF) in Oracle RAC?
TAF enables a client session to automatically reconnect to another node in case of a failure, ensuring minimal disruption.
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What is the difference between Oracle RAC and distributed data?
There is no difference between RAC and distributed data, as RAC is a clustered environment.
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What are some RAC specific parameters ?
- Undo Management
undo_tablespaces
– Defines the UNDO tablespace for each RAC instance.
- Cluster Configuration
cluster_database
– Enables Oracle RAC functionality.cluster_database_instances
– Specifies the number of instances in the RAC cluster.
- Interconnect & Communication
cluster_interconnects
– Defines the private network for RAC interconnect traffic.remote_listener
– Specifies the SCAN listener for dynamic service registration.
- Instance & Redo Management
thread
– Assigns a redo log thread to each instance.
- Undo Management
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What is a Service in Oracle RAC?
A service in Oracle RAC is a logical database connection point that allows workload management and high availability for applications.
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What is Dynamic Resource Manager (DRM) in Oracle RAC?
DRM dynamically moves resources such as buffer cache between instances to optimize performance based on workload.
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What is nodeapps?
Nodeapps are standard set of oracle application services which are started automatically for RAC.
Node apps Include: vip,network,adminhelper,ONS
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What is this recovery buddy feature in oracle 19c?
The Recovery Buddy feature in Oracle 19c improves Data Guard recovery performance by distributing redo apply workload across multiple instances in an Active Data Guard environment. It allows one instance (the apply instance) to offload redo block fetching and apply processing to another instance (the recovery buddy) in an Oracle RAC standby database. This reduces contention on the apply instance and improves redo apply efficiency, especially in multi-instance standby configurations.
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What will happen if I kill the database archiver process in oracle rac node?
It will be restarted.
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What is application continuity and transactional dataguard in oracle rac?
Application Continuity (AC) in Oracle RAC ensures that transactions are automatically retried and masked from users in case of planned or unplanned failures. It replays in-flight transactions after a failure, ensuring session persistence without user disruption.
Transactional Data Guard (TDG) allows a standby database to process read-only queries and transactions while continuously applying redo from the primary database. This enables real-time reporting and offloads workload from the primary database while maintaining high availability.
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What is the concept of a cluster in the context of Oracle R A C?
A cluster refers to a group of interconnected nodes acting as a single system, and it is essential for applications that want to be highly available and are deployed in clusters, even in cloud environments.
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What is a Voting Disk in Oracle RAC?
A voting disk is a shared disk used to determine which nodes in the cluster are active and to prevent split-brain scenarios.
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What is the purpose of the Oracle RAC Database Rolling Patch and Rolling Patch Plan features?
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What is an OCR (Oracle Cluster Registry)?
OCR is a repository that stores cluster configuration details, including node membership, voting disk information, and resource profiles.
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Why is Oracle RAC crucial for highly available environments?
Oracle RAC is crucial for highly available environments, especially for those working on databases or upgrading to R A C.
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Why RAC has separate redo thread for each node?
In RAC, each instance have their own lgwr process , So there has to be separate online redolog for each instance ( called as thread), So that lgwr will write to the respective redo log.
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What is a Private Interconnect in Oracle RAC?
A private interconnect is a dedicated, high-speed network used for communication between RAC instances.
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What are the three types of IP addresses in the RAC environment?
The three types of IP addresses are public, private, virtual, SCN, and SCN.
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Explain the role of the Fast Application Notification (FAN) in Oracle RAC.
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What is SCAN (Single Client Access Name) in Oracle RAC?
SCAN provides a single access point for database connections in RAC. It simplifies connection management and supports automatic failover and load balancing.
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What are the key benefits of using Oracle Rack for high availability and scalability?
Oracle Rack allows for increased user connections, efficient database management, and improved performance, as well as the ability to add additional nodes for increased capacity without requiring any application changes.
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What are the types of services in Oracle RAC?
Database Service: Logical representation of a workload to distribute connections.
VIP (Virtual IP) Service: Provides failover support for client connections. -
How does Oracle RAC handle contention for resources among instances, and what is the role of Global Enqueues?
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Explain Oracle Flex Clusters.
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Why RAC has separate undo tablespace for each node?
Oracle RAC requires a separate UNDO tablespace for each instance to:
- Avoid contention – Prevents multiple instances from accessing the same undo segments.
- Ensure read consistency – Each instance maintains its own undo for queries and recovery.
- Improve performance – Reduces inter-instance communication and undo block conflicts.
- Enable faster recovery – Each instance handles its own undo during crash recovery.
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What is a Virtual IP (VIP) in Oracle RAC?
A VIP is an IP address that is assigned to a RAC node and fails over to another node if the original node goes down, ensuring uninterrupted client connections.
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What is Transparent Application Failover (TAF)?
TAF allows a client session to reconnect to another RAC instance automatically if the original connection fails.
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Can i have 7 voting disks in a 3 node RAC? Let’s say in your grid setup currently only 3 voting disks are present. How can we make it 7?
Yes, you can have 7 voting disks in a 3-node RAC, as Oracle allows an odd number of voting disks (1, 3, 5, 7, etc.) for quorum-based failure handling.
To increase from 3 to 7 voting disks, use the following command:
$ crsctl replace votedisk +<DISKGROUP>
This replaces existing voting disks and automatically adjusts the count based on ASM redundancy. Alternatively, to manually add disks:
$ crsctl add votedisk +<DISKGROUP>/<VOTING_DISK_FILE>
Verify the change using:
$ crsctl query css votedisk
Restart Clusterware if required:
$ crsctl stop crs $ crsctl start crs
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Suppose someone has changed the permission of files inside grid_home. How you will fix it?
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What data we need to check in vmstat and iostat output?
vmstat
(CPU & Memory Performance)- r (Run Queue) – High values indicate CPU bottlenecks.
- us, sy, id, wa (CPU Usage) – High
%wa
(I/O wait) suggests disk issues. - si, so (Swap In/Out) – Frequent swapping indicates memory pressure.
iostat
(Disk I/O Performance)- %util – If near 100%, disk is overloaded.
- await (Average Wait Time) – High values indicate slow I/O performance.
- svctm (Service Time) – Should be low; high values suggest storage issues.
- tps (Transactions per Second) – Indicates disk activity level.
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What is a split brain?
When database nodes in a cluster are unable to communicate with each other, they may continue to process and modify the data blocks independently. If the same block is modified by more than one instance, synchronization/locking of the data blocks does not take place and blocks may be overwritten by others in the cluster. This state is called split brain.
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What is the difference between Crash recovery and Instance recovery?
When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC environment, the same recovery for an instance is performed by the surviving nodes called Instance recovery.
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What utility allows for checking flex mode and cluster mode in Oracle Clusterware?
The ASM CMD utility is used to check flex mode and cluster mode in Oracle Clusterware.
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What benefits does Oracle Clusterware architecture offer?
Oracle Clusterware architecture offers benefits such as reduced system contention and loads, improved scalability, reduced costs on security infrastructure management, and low-cost hardware.
It also allows for more scalable applications, the ability to fail over nodes, increased throughput on demand, and the ability to monitor and restart processes.
Data centre server roomThe ASM CMD utility is used to check flex mode and cluster mode in Oracle Clusterware. -
What is Flex Cluster introduced in oracle 12c?
Flex Cluster (introduced in Oracle 12c) is an enhanced RAC architecture with two types of nodes:
- Hub Nodes – Perform database processing and maintain full cluster functionality.
- Leaf Nodes – Lightweight nodes that rely on hub nodes for cluster management and only run applications or ASM clients.
Advantages:
Scalability – Supports large-scale deployments.
Reduced Interconnect Traffic – Leaf nodes do not participate in cache fusion.
Improved Resource Utilization – Ideal for applications that do not need full cluster services. -
Explain the use of interconnect?
It is a private network that is used to ship data blocks from one instance to another for cache fusion. The physical data blocks, as well as data dictionary blocks, are shared across this interconnect.
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What is ACMS?
ACMS stands for Atomic Controlfile to Memory Service. It synchronizes the control file updates across Oracle Real Application Clusters (RAC) instances, ensuring consistency and high availability of database metadata.
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How do you determine what protocol is being used for Interconnect traffic?
One of the ways is to look at the database alert log for the time period when the database was started.
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Why is it important to create a separate ATL home on each instance when installing Oracle Rac?
Creating a separate ATL home on each instance allows for better management advantages, out-of-place patching, and eliminating database downtime in multi-node cluster environments.
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Can we start crs in exclusive mode? and its purpose?
Yes, Oracle Clusterware (CRS) can be started in exclusive mode. It is used for maintenance tasks, troubleshooting, and ensuring isolation of a single node from the cluster to perform critical operations without affecting other nodes’ services.
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What methods are available to keep the time synchronized on all nodes in the cluster?
Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
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What is Oracle Flex ASM and what are its benefits?
Oracle Flex ASM is a feature that allows for managing Oracle ASM instances on separate physical servers, supporting larger cluster setups, and reducing Oracle ASM portrayer or other systems.
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What is the role of LMON background process?
The LMON (Global Enqueue Service Monitor) background process in Oracle RAC manages and monitors global resources, including global enqueue locks and resources. It helps ensure consistency and coordination across multiple instances in the RAC cluster by managing distributed lock management and resolving lock conflicts
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What file components in RAC must reside on shared storage?
Spfiles, ControlFiles, Datafiles, and Redolog files should be created on shared storage.
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If crs is not coming up , then what are things you will start looking into?
If CRS is not coming up, I would start by checking logs, reviewing alert logs, verifying dependencies, checking disk space, reviewing configuration files, verifying permissions, checking cluster interconnect, reviewing OS logs, checking cluster health, and investigating hardware failures.
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Where does the Clusterware write when there is a network or Storage missed heartbeat?
The network ping failure is written in $CRS_HOME/log
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How do you find out what OCR backups are available?
The OCR config – shows backup can be run to find out the automatic and manually run backups.
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Explain about local_listener and remote_listener parameter in RAC?
Local_listener:
Definition: This parameter specifies the network address that an Oracle RAC instance uses to listen for local connection requests.
Purpose: The local listener is responsible for managing connection requests originating from the same node where the instance is running.
Configuration: The local_listener parameter is set to a TNS entry or a net service name that resolves to a network address (hostname and port) where the local listener is running.
ALTER SYSTEM SET LOCAL_LISTENER = ‘mydb_listener’ SCOPE=both;
Here, ‘mydb_listener’ is a TNS entry pointing to the local listener’s address.
Remote_listener:
Definition: This parameter specifies one or more network addresses that an Oracle RAC instance uses to listen for remote connection requests from other instances in the cluster.
Purpose: The remote listener facilitates communication between instances on different nodes in the RAC cluster.
Configuration: The remote_listener parameter is set to a list of TNS entries or net service names that resolve to network addresses (hostnames and ports) where the remote listeners are running on other nodes in the cluster.
ALTER SYSTEM SET REMOTE_LISTENER = ‘node1_listener, node2_listener’ SCOPE=both;
Here, ‘node1_listener’ and ‘node2_listener’ are TNS entries pointing to the remote listeners on different nodes.
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If your OCR is corrupted what options do have to resolve this?
You can use either the logical or the physical OCR backup copy to restore the Repository.
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How do you find out what object has its blocks being shipped across the instance the most?
You can use the dba_hist_seg_stats.
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What is client side load balancing and server side load balancing?
Client-side load balancing: Clients distribute requests across multiple servers, deciding which server to connect to based on various algorithms such as round-robin or least connections.
Server-side load balancing: Load balancing is handled by a dedicated device or software component, such as a load balancer or proxy server, which distributes incoming requests among multiple servers based on predefined algorithms and server health checks.
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What is the role of ASM and ASM Volume Manager in managing data-based clients in a multi-node cluster environment?
ASM and ASM Volume Manager are essential components for managing data-based clients in a multi-node cluster environment, optimizing database management, and reducing the need for Oracle ASM portraver or other systems.
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How do we know which database instances are part of a RAC cluster?
You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.
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What are the RAC related background processes?
LMSn (Lock Manager Server): Manages global resource coordination and distributed locks across RAC instances.
LMD (Lock Manager Daemon): Coordinates lock-related messaging among RAC instances and manages lock conversion requests.
LMON (Global Enqueue Service Monitor): Monitors global resources and manages global enqueue services, such as space allocation for global resources.
LMSn (Global Cache Service Process): Handles cache fusion operations by transferring data blocks between RAC instances to maintain cache coherence.
GCR (Global Cache Service Resources): Coordinates global cache resources and manages cache fusion and resource requests.
GCS (Global Cache Service): Manages the global cache and facilitates cache fusion operations between RAC instances.
RMSn (Resource Manager Server): Controls resource allocation and prioritization for database sessions based on resource management policies.
RBAL (Rebalance): Coordinates instance and resource rebalancing operations to maintain workload distribution across RAC instances.
MMON (Manageability Monitor): Monitors database and instance health, collecting statistics and managing advisory components.
MMNL (Manageability Monitor Light): Light version of MMON for low-priority monitoring tasks.
DIA0 (Diagnosability Process): Handles diagnostic data collection and monitoring for cluster-related issues.
LREG (Local Enqueue Service Registration): Registers local enqueue services with the Global Cache Service (GCS).
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What are the advantages of distribution in Oracle RAC?
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What is OCLUMON used for in a cluster environment?
The Cluster Health Monitor (CHM) stores operating system metrics in the CHM repository for all nodes in a RAC cluster. It stores information on CPU, memory, process, network, and other OS data, This information can later be retrieved and used to troubleshoot and identify any cluster-related issues.
It is a default component of the 11gr2 grid install. The data is stored in the master repository and replicated to a standby repository on a different node.
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Tell about thethe role of Google Net Services client access in Oracle RAC?
Google Net Services client access is used to distribute connection requests across multiple instances in Oracle R A C.
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Can i have 7 voting disks in a 3 node RAC? Let’s say in your grid setup currently only 3 voting disks are present. How can we make it 7?
Yes, you can have 7 voting disks in a 3-node RAC, as Oracle allows an odd number of voting disks (1, 3, 5, 7, etc.) for quorum-based failure handling.
To increase from 3 to 7 voting disks, use the following command:
$ crsctl replace votedisk +<DISKGROUP>
This replaces existing voting disks and automatically adjusts the count based on ASM redundancy. Alternatively, to manually add disks:
$ crsctl add votedisk +<DISKGROUP>/<VOTING_DISK_FILE>
Verify the change using:
$ crsctl query css votedisk
Restart Clusterware if required:
$ crsctl stop crs $ crsctl start crs
Would you like guidance on best practices for voting disk placement?
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What would be the possible performance impact in a cluster if a less powerful node (e.g. slower CPUs) is added to the cluster?
All processing will show down to the CPU speed of the slowest server.
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How instance recovery happens in oracle RAC?
When any one of the instance is crashed in RAC, then this node failure is detected by the surviving instances. Now the GRD resouces will be distributed across the existing instances. The instance which first detects the crash, will the start the online redo log thread of the crashed instance. The SMON of that instance.
Sequence
- Normal RAC operation, all nodes are available.
- One or more RAC instances fail.
- Node failure is detected.
- Global Cache Service (GCS) reconfigures to distribute resource management to the surviving instances.
- The SMON process in the instance that first discovers the failed instance(s) reads the failed instance(s) redo logs to determine which blocks have to be recovered.
- SMON issues requests for all of the blocks it needs to recover. Once all blocks are made available to the SMON process doing the recovery, all other database blocks are available for normal processing.
- Oracle performs roll forward recovery against the blocks, applying all redo log recorded transactions.
- Once redo transactions are applied, all undo records are applied, which eliminates non-committed transactions.
- Database is now fully available to surviving nodes. will read the redo to do rollforward ( i.e to apply both committed and noncommited data). Once rollforward is done, it will rollback the uncommited transactions using UNDO tablespace of the failed instance.
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What is the default memory allocation for ASM?
In 10g the default SGA size is 1G in 11g it is set to 256M and in 12c ASM it is set back to 1G.
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What is Data Guard and how does it relate to Oracle?
Data Guard is a feature in Oracle that provides disaster recovery solutions.
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How does Oracle RAC manage and distribute redo log entries across instances?
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How does Oracle RAC handle data consistency during write operations, and what is the role of the Global Cache Service (GCS)?
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How do you back up ASM Metadata?
You can use md_backup to restore the ASM disk group configuration in case of ASM disk group storage loss.
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What files can be stored in the ASM disk group?
In 11g the following files can be stored in ASM disk groups.
- Datafiles
- Redo logfiles
- Spfiles
In 12c the files below can also now be stored in the ASM Diskgroup
- Password file
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What is the ASM POWER_LIMIT?
This is the parameter that controls the number of Allocation units the ASM instance will try to rebalance at any given time. In ASM versions less than 11.2.0.3 the default value is 11 however it has been changed to unlimited in later versions.
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Can we have multiple SCAN(name) in a RAC?
From 12c onwards, We can have multiple scan with different subnets. As part of installation only scan will be configured. Post installation we need to configure another SCAN with different subnet( If required).
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What is a rolling upgrade?
Ans: A patch is considered rolling if it is can be applied to the cluster binaries without having to shut down the database in a RAC environment. All nodes in the cluster are patched in a rolling manner, one by one, with only the node which is being patched unavailable while all other instances open.
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What are some of the RAC-specific parameters?
Some of the RAC parameters are:
- CLUSTER_DATABASE
- CLUSTER_DATABASE_INSTANCE
- INSTANCE_TYPE (RDBMS or ASM)
- ACTIVE_INSTANCE_COUNT
- UNDO_MANAGEMENT
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In RAC, where we define the SCAN?
We can define SCAN with below 2 option.
Using corporate DNS
Using Oracle GNS( Grid naming service)
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What is the future of the Oracle Grid?
The Grid software is becoming more and more capable of not just supporting HA for Oracle Databases but also other applications including Oracle’s applications. With 12c there are more features and functionality built-in and it is easier to deploy these pre-built solutions, available for common Oracle applications.
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What components of the Grid should I back up?
The backups should include OLR, OCR, and ASM Metadata.
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Is there an easy way to verify the inventory for all remote nodes?
You can run the OPATCH LSINVENTORY -ALL_NODES command from a single node to look at the inventory details for all nodes in the cluster.
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What g stand for in views like gv$session , gv$sql etc.?
In Oracle Database, the “g” in views like gv$session, gv$sql, and similar views stands for “Global.” These views provide a global or cluster-wide perspective of database activity and resources in Oracle Real Application Clusters (RAC) environments.
The “gv” prefix indicates that these views are “Global Views,” meaning they aggregate information from all instances in the RAC cluster. They allow administrators and users to monitor and manage database resources and activities across all nodes in the cluster from a single point of access.
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Why should we have seperate homes for ASm instance?
Ans:It is a good practice to have ASM home seperate from the database hom(ORACLE_HOME).This helps in upgrading and patching ASM and the Oracle database software independent of each other.Also,we can deinstall the Oracle database software independent of the ASM instance.
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What is the advantage of using ASM?
Having ASM is the Oracle recommended storage option for RAC databases as the ASM maximizes performance by managing the storage configuration across the disks.ASM does this by distributing the database file across all of the
available storage within our cluster database environment. -
What are local registry and cluster registry in RAC Architecture?
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How is the data architecture connected to the front end in RAC Architecture?
In Oracle RAC architecture, the data layer (database nodes) is connected to the front-end (applications, users, or web servers) through multiple network components ensuring high availability, load balancing, and seamless access to data.
Users or applications connect to the RAC database using SCAN (Single Client Access Name), which provides a single entry point for the cluster. SCAN resolves to multiple IP addresses that are distributed across the available database nodes, allowing automatic load balancing and failover. Each RAC node has a Virtual IP (VIP) that redirects connections if a node fails, ensuring continuous availability.
The Oracle Net Listener on each node handles client requests and routes them to the appropriate instance. Additionally, Load Balancing Advisory and Services optimize traffic distribution, ensuring that application queries are processed efficiently across all nodes. This architecture ensures that the front end remains connected to the database with minimal disruption, even if a node goes down.
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List out the difference between a public and private subnet in RAC Architecture?
The public subnet is used for external communication, while the private subnet is used for internal communication within the rack.
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What happens if an application connects to a different node in RAC Architecture?
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Define a CHF framework in RAC Architecture?
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Why is the VIP concept important in RAC Architecture?
The VIP concept is important because it allows for the rack connection to be handed over to the existing or surviving node in case of node failure, ensuring high availability and reliability.
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What is gc cr 2 way and gc cr 3 way?
gc cr 2-way (Global Cache Consistent Read 2-way):
This wait event occurs when an instance in the RAC environment is waiting for a consistent read block from another instance.
It indicates contention between two instances for access to the same consistent read block in the global cache.
The number “2-way” signifies that the contention is between two instances.
gc cr 3-way (Global Cache Consistent Read 3-way):
Similar to “gc cr 2-way”, this wait event occurs when an instance is waiting for a consistent read block from another instance.
However, “gc cr 3-way” indicates contention among three instances for access to the same consistent read block in the global cache.
It signifies contention between three instances.
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What is the role of database listeners in RAC Architecture?
Database listeners usually listen under VIP addresses, but if a node goes down, the client needs to switch over their connections to maintain availability.
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Explain the role of the Global Resource Directory (GRD) in Oracle RAC.
The Global Resource Directory (GRD) is a key component of Oracle RAC’s Global Cache Service (GCS). It maintains metadata about database blocks and their statuses across all RAC instances.
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How do you add a node to an existing Oracle RAC cluster?
To add a node to an existing Oracle RAC cluster, you need to install the Oracle Grid Infrastructure software on the new node, configure the network settings, and use the addNode.sh script to extend the cluster to include the new node.
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What will happen if I kill the ohasd process in oracle rac node?
If you kill the OHASD (Oracle High Availability Services Daemon) process in an Oracle RAC node, all Clusterware resources on that node, including CRS, CSSD, and ASM, will stop. The node will be evicted from the cluster if other nodes detect the failure. Oracle Clusterware may attempt to restart OHASD, but if it fails to recover, the node may require a manual restart to rejoin the cluster. This can impact database availability and cluster stability.
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What will happen if I kill the crs process in oracle rac node?
If you kill the CRS (Cluster Ready Services) process in an Oracle RAC node, all cluster-related services on that node, including CSSD (Cluster Synchronization Services), CRSD (Cluster Resource Services), and OHASD (Oracle High Availability Services Daemon), will stop. This will cause the node to lose communication with the cluster, leading to node eviction if other nodes detect the failure. The node will either reboot automatically or require a manual restart to rejoin the cluster, affecting database and application availability.
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Explain the concept of Oracle RAC Connection Affinity.
Oracle RAC Connection Affinity allows administrators to configure preferred instances for specific services. Clients can connect to these preferred instances, optimizing resource utilization and enhancing connection efficiency. This feature provides greater control over how client connections are distributed across the Oracle RAC cluster, contributing to improved performance and resource management.
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Is dynamic remastering good or bad?
Dynamic remastering in Oracle RAC is generally good as it helps improve performance by relocating Global Enqueue Resources (GEs) to the instance that most frequently accesses them. This reduces inter-instance communication and global cache waits. However, excessive or frequent remastering can cause performance overhead due to the continuous movement of resources. Proper workload distribution and segment affinity tuning are essential to ensure efficient dynamic remastering without unnecessary overhead.
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I have a 3 node RAC. where node 1 is master node. If node 1 is crashed. Then out of node2 and node3 , which node will become master?
In a 3-node RAC, if Node 1 (master) crashes, the new master will be the node with the lowest node ID among the surviving nodes (Node 2 or Node 3). Oracle Clusterware uses Node Membership Services (NMS) to elect the new master, preferring the lowest-numbered node.
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What is Oracle RAC Direct NFS (dNFS)?
Oracle RAC Direct NFS (dNFS) is a feature enhancing I/O performance in Oracle RAC environments. It enables direct communication between database instances and NFS storage servers. By bypassing the operating system’s NFS client, dNFS reduces I/O latency and improves overall storage efficiency. It enhances scalability and performance by optimizing the interaction between Oracle RAC nodes and NFS storage.
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What is the purpose of the Oracle RAC Database Rolling Upgrade Out of Place feature?
The Rolling Upgrade Out of Place feature allows administrators to perform a rolling upgrade of an Oracle RAC database by creating a new Oracle home and database while the existing one remains operational. This ensures minimal downtime and a smooth transition to the upgraded environment.
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Suppose I am running a insert statement by connecting to a database using service . And if that instance is crashed, then what will happen to the insert statement?
If the instance hosting the service crashes while you are running an INSERT statement, the transaction will be rolled back because the session is lost. Oracle RAC will automatically failover the service to an available instance, but your session will be disconnected. You will need to reconnect and re-execute the INSERT statement. If TAF (Transparent Application Failover) or Application Continuity is configured, Oracle can retry the transaction automatically, depending on the failover settings.
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What is the significance of the Oracle RAC Multi-Instance Redo Log feature?
- Multi-Instance Redo Log enables instances to write to multiple redo log groups concurrently, improving performance.
- It reduces contention for the redo log and enhances scalability in write-intensive workloads in Oracle RAC.
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What is the purpose of the Oracle RAC Wait Events in performance tuning?
Oracle RAC Wait Events provide detailed information about the reasons for performance bottlenecks. By analyzing these events, administrators can identify resource-intensive operations, monitor wait times, and take corrective actions to optimize the performance of the Oracle RAC database.
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Can there be gc-4-way wait events in 4 node rac?
No, in a 4-node RAC, you won’t see gc-4-way wait events. Oracle RAC uses gc-2-way and gc-3-way wait events when blocks are transferred between instances. A gc-4-way event would imply coordination among four instances simultaneously, which does not happen. Instead, blocks are transferred in a point-to-point manner between instances, leading to gc-2-way (two instances involved) or gc-3-way (three instances involved) waits.
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What is preferred and available in a service in RAC?
In Oracle RAC, a preferred instance for a service is the instance where the service is intended to run under normal conditions. An available instance is a backup instance that runs the service only if the preferred instance fails.
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Explain the concept of the Oracle RAC Database Rolling Downgrade.
- Rolling Downgrade allows administrators to revert an Oracle RAC database to a previous release without downtime.
- It involves downgrading individual nodes one at a time while the rest of the cluster remains operational.