What is RAC?
RAC stands for Real Application cluster.
It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.
Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide a highly scalable and available database solution for all the business applications.
Oracle RAC provides the foundation for enterprise grid computing.
What is Oracle RAC One Node?
Oracle RAC one Node is a single instance running on one node of the cluster while the 2nd node is in cold standby mode. If the instance fails for some reason then RAC one node detect it and restart the instance on the same node or the instance is relocate to the 2nd node incase there is failure or fault in 1st node. The benefit of this feature is that it provides a cold failover solution and it automates the instance relocation without any downtime and does not need a manual intervention. Oracle introduced this feature with the release of 11gR2 (available with Enterprise Edition).
What are Oracle RAC Components?
VIP, Node apps etc.
What are Oracle Cluster Components?
- Cluster Interconnect (HAIP)
- Shared Storage (OCR/Voting Disk)
- Clusterware software
- Oracle Kernel Components
What are the advantages of RAC (Real Application Clusters)?
Reliability – if one node fails, the database won’t fail
Availability – nodes can be added or replaced without having to shutdown the database
Scalability – more nodes can be added to the cluster as the workload increases
How you check the health of Your RAC Database?
‘crsctl’ command from root or oracle user can be used to check the clusterware health But for starting or stopping we have to use root user or any privilege user.
[oracle@TEST_NODE1 ~]$ crsctl check crs
CSS appears healthy
CRS appears healthy
EVM appears healthy
How you check the services in RAC Node?
We can check the service or start the services with ‘srvctl’ command.load balanced/TAF service named RAC online.
[oracle@TEST_NODE1 ~]$ srvctl start service -d orcl -s RAC
[oracle@TEST_NODE1 ~]$ crsstat
How you will backup your RAC Database?
Backup strategy of RAC Database:
An RAC Database consists of OCR, Voting disk & Database files, controlfiles, redolog files & Archive log files.
What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using the below
- OEM (Enterprise Manager),
- Server control (SRVCTL),
- Cluster Verification Utility (CLUVFY),
What is Clusterware?
Software that provides various interfaces and services for a cluster. Typically, this includes capabilities that:
- Allow the cluster to be managed as a whole
- Protect the integrity of the cluster
- Maintain a registry of resources across the cluster
- Deal with changes to the cluster
- Provide a common view of resources
What are Oracle Clusterware Components?
Voting Disk – Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.
Oracle Cluster Registry (OCR) – Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster
How to control Oracle Clusterware?
To start or stop Oracle Clusterware on a specific node:
# crsctl stop crs
# crsctl start crs
To enable or disable Oracle Clusterware on a specific node:
# crsctl enable crs
# crsctl disable crs
What is the purpose of Private Interconnect?
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes. This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster.
What is GNS?
Grid Naming service is alternative service to DNS, which will act as a sub domain in your DNS but managed by Oracle, with GNS the connection is routed to the cluster IP and manages internally.
What is GRD?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each data file and each cached block using global resource directory. This process is referred to as cache fusion and helps in data integrity.
What is SCAN listener?
A scan listener is something that additional to node listener which listens the incoming db connection requests from the client which got through the scan IP, it got end points configured to node listener where it routes the db connection requests to particular node listener.
What is GSDCTL in RAC? list GSDCTL commands in Oracle RAC?
GSDCTL stands for Global Service Daemon Control, we can use gsdctl commands to start, stop, and obtain the status of the GSD service on any platform.
The options for gsdctl are:-
$ gsdctl start — To start the GSD service
$ gsdctl stop — To stop the GSD service
$ gsdctl stat — To obtain the status of the GSD service
Log file location for gsdctl:
What is SCAN?
Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.
What is dynamic remastering? When will the dynamic remastering happens?
Dynamic remastering is ability to move the ownership of resource from one instance to another instance in RAC. dynamic resource remastering is used to implement for resource affinity for increased performance. resource affinity optimized the system in situation where update transactions are being executed in one instance. when activity shift to another instance the resource affinity correspondingly moves to another instance. If activity is not localized, then resource ownership is hashed to the instance.
In 10g dynamic remastering happens in file +object level. the process of remastering is very stringent. For one instance should touch more than 50 times than the other instance in particular period (say 10 mints). this touch ratio and time can be tuned by gc_affinity_limit and _gc_affinity_time parameter.
What is cache fusion?
In a RAC environment, it is the combining of data blocks, which are shipped across the interconnect from remote database caches (SGA) to the local node, in order to fulfill the requirements for a transaction (DML, Query of Data Dictionary).
What is a CFS?
A cluster File System (CFS) is a file system that may be accessed (read and write) by all members in a cluster at the same time. This implies that all members of a cluster have the same view.
What is an OCFS2?
The OCFS2 is the Oracle (version 2) Cluster File System which can be used for the Oracle Real Application Cluster.
What is a raw device?
A raw device is a disk drive that does not yet have a file system set up. Raw devices are used for Real Application Clusters since they enable the sharing of disks.
What is a raw partition?
A raw partition is a portion of a physical disk that is accessed at the lowest possible level. A raw partition is created when an extended partition is created and logical partitions are assigned to it without any formatting. Once formatting is complete, it is called cooked partition.
What is CRS?
Oracle RAC 10g Release 1 introduced Oracle Cluster Ready Services (CRS), a platform-independent set of system services for cluster environments. In Release 2, Oracle has renamed this product to Oracle Clusterware.
What is the use of OCR?
Oracle Clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR (Oracle Cluster Registry).
What is the Load Balancing Advisory?
To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory. This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage value of how much of the total workload should be sent to this instance as well as service quality flag.
What is the Cluster Verification Utiltiy (cluvfy)?
The Cluster Verification Utility (CVU) is a validation tool that you can use to check all the important components that need to be verified at different stages of deployment in a RAC environment.
What is O2CB?
The O2CB is the OCFS2 cluster stack. OCFS2 includes some services. These services must be started before using OCFS2 (mount/ format the file systems).