Here we have mentioned most frequently asked DBA/RAC Interview Questions and Answers specially for freshers and experienced.
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The Clusterware is installed on each node (on an Oracle Home) and on the shared disks (the voting disks and the CSR file)
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The base software is installed on each node of the cluster and the database storage on the shared disks.
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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.
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The OCFS2 is the Oracle (version 2) Cluster File System which can be used for the Oracle Real Application Cluster.
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Note: There are some platform specific limitations.
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HP Tru64 Unix, Veritas, Microsoft
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This is possible by using a raw device.
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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.
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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.
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A CFS offers:
Note: This option is very dependent on the availability of a CFS on your platform.
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Note: Autoextend fails on raw devices if the space is exhausted. However the space could be added online if needed.
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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.
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It returns a dead connection IMMIDIATELY, when its primary node fails. Without using VIP IP, the clients have to wait around 10 minutes to receive ORA-3113: “end of file on communications channel”. However, using Transparent Application Failover (TAF) could avoid ORA-3113.
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SSH (Secure Shell,10g+) or RSH (Remote Shell, 9i+) allows “oracle” UNIX account connecting to another RAC node and copy/ run commands as the local “oracle” UNIX account.
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No. SSH or RSH are needed only for RAC, patch set installation and clustered database creation.
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Each node of a cluster that is being used for a clustered database will typically have the RDBMS and RAC software loaded on it, but not actual data files (these need to be available via shared disk).
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The SID prefix in 10g Release 1 and prior versions was restricted to five characters by install/ config tools so that an ORACLE_SID of up to max of 5+3=8 characters can be supported in a RAC environment. The SID prefix is relaxed up to 8 characters in 10g Release 2, see bug 4024251 for more information.
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The Real Application Clusters do not support heterogeneous platforms in the same cluster.
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RAC and Clusterware deployment best practices suggests that the interconnect (private connection) be deployed on a stand-alone, physically separate, dedicated switch. On big network the connections could be instable.
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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.
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With 10g Release 2, we support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database. Currently DBCA has a bug where it will not go beyond 63 instances. There is also a documentation bug for the max-instances parameter. With 10g Release 1 the Maximum is 63.
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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.
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The cluster verification utility is release with Oracle Database 10g Release 2 but can also be used with Oracle Database 10g Release 1.
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Yes. When certified, you can use Vendor Clusterware however you must still install and use Oracle Clusterware for RAC. Best Practice is to leave Oracle Clusterware to manage RAC. For details see Metalink Note 332257.1 and for Veritas SFRAC see 397460.1.
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Yes.
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The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.
There are 2 key parameters for this module:
-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends setting it to 30seconds.
-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.
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Yes.
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For optimal performance, you should only put the following files on Linux OCFS2:
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No, the OCR and voting disk must be on raw or CFS (cluster file system).
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No, you must properly uninstall Oracle Clusterware and then re-install.
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The O2CB is the OCFS2 cluster stack. OCFS2 includes some services. These services must be started before using OCFS2 (mount/ format the file systems).
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OCR is a file that manages the cluster and RAC configuration.
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The voting disk is nothing but a file that contains and manages information of all the node memberships.
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RMAN to make backups of the database, dd to backup your voting disk and hard copies of the OCR file.
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crs_stat -t -v (-t -v are optional)
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You can create a RAC with just one server.
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RAC processes are: LMON, LMDx, LMSn, LKCx and DIAG.
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Yes, but Clusterware version must be greater than the greater database version.
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OPS: Oracle Parallel Server
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Private Interconnect.
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A RAC view has the prefix ‘G’. For example, GV$SESSION instead of V$SESSION
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srvctl
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A- One for each instance.
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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
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#dd if=voting_disk_name of=backup_file_name
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#crsctl query css votedisk
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check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)
or
#ocrcheck
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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.
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A cluster is referred to a group of independent, but connected servers that behaves as a single system.
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RAC or Real Application Cluster is a component of the database product that enables the database to be installed across multiple servers. Oracle RAC uses Oracle Clusterware for the infrastructure to bind multiple servers, so they operate as a single system.
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The main elements of an Oracle RAC system are,
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Benefits of RAC is that
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The file storage options provided by Oracle Database for Oracle RAC are,
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Volume management techniques used in Oracle RAC is that,
Oracle RAC provides dynamic volume manager. It has a file system that consists of information of the cluster file system
Cluster file system in Oracle is known as OCFS. It has the connection with the databases that provide raw devices and command line features.
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The new feature added in Oracle ASM 12c is Oracle Flex ASM. Its a new ASM deployment model which increases instance database availability and reduces the Oracle ASM related resource consumption.
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Oracle Flex ASM instance when fails on a particular node, then the Oracle Flex ASM instance is passed over to another node in the cluster.
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The key characteristics of RAC are,
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Cache function is used to show the storage of the information in the clustered network with the Oracle database. It involves two nodes, one writes the data to the same disk, and other reads the data block from the disk. For its network connection, RAC uses a dedicated server for its network, and cache function is an internal part of the cluster.
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Single Instance Environment | RAC Environment |
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In Oracle RAC, all the instances/servers communicate with each other using a private network. When the instance members in a RAC fail to ping/connect to each other via this private network and continue to process data block independently. Then this process is referred as Split Brain Syndrome.
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If you keep split brain syndrome unresolved, then there would be data integrity issue. The blocks changed in one instance will not be locked and could be over-written by another instance. It is resolved by using the voting disk, it will decide which node(s) will survive and which node(s) will be evicted.
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To determine what protocol is being used for Interconnect traffic you can look at the database alert log for the time period when the database was started up.
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In RAC ControlFiles, Spfiles, Redolog files, and Datafiles should be created on shared storage.
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When there is a network or storage issue the network ping failure is written in $CRS_HOME/log
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Tools provided in Oracle Enterprise Manager are,
Grid Control-
Database Control-
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A crash recovery takes place when an instance crashes in a single node database on startup. When the same recovery for an instance is performed in RAC environment by the surviving nodes then it is called Instance recovery.
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if your OCR is corrupted, you can either use the logical or physical OCR backup copy to restore the repository.
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ORL stands for Oracle Local Repository (OLR). It consists of information which enables the cluster programs to initiate with the OCR in the ASM Storage. Until the grid process are started, the ASM file is unavailable. In such case, a local copy of the data of the OCR is required, that is stored in OLR.
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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).
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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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When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC enviornment the same recovery for an instance is performed by the surviving nodes called Instance recovery.
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It is a private network which 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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One of the ways is to look at the database alert log for the time period when the database was started up.
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Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
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Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.
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The network ping failure is written in $CRS_HOME/log
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The ocrconfig -showbackup can be run to find out the automatic and manually run backups.
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You can use either the logical or the physical OCR backup copy to restore the Repository.
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You can use the dba_hist_seg_stats.
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The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.
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You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.
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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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All processing will show down to the CPU speed of the slowest server.
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Oracle Local repository contains information that allows the cluster processes to be started up with the OCR being in the ASM storage ssytem. Since the ASM file system is unavailable until the Grid processes are started up a local copy of the contents of the OCR is required which is stored in the OLR.
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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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You can use md_backup to restore the ASM diskgroup configuration in-case of ASM diskgroup storage loss.
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In 11g the following files can be stored in ASM diskgroups.
1. Datafiles
2. Redo logfiles
3. Spfiles
In 12c the files below can also new be stored in the ASM Diskgroup
1. Password file
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This is the parameter which 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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A patch is considered a rolling if it is can be applied to the cluster binaries without having to shutting 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 instance open.
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Some of the RAC parameters are:
1. CLUSTER_DATABASE
2. CLUSTER_DATABASE_INSTANCE
3. INSTANCE_TYPE (RDBMS or ASM)
4. ACTIVE_INSTANCE_COUNT
5. UNDO_MANAGEMENT
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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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Oracle RAC uses a single system in the form of an image to configure and manage the servers in an easy way. It provides a database for the installed and configured applications from one location so that it can be managed in an easy way.
The components required to be provided with it is as follows:
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Cluster Verification Utility is a tool in the Oracle Grid that is used to eliminate the errors that come up with the validations of the steps.
It provides the verification on the changes that is being made in the configuration of the files or the system.
The tool can be used with the command line interface and it is used to validate the configuration input as well such that during the installation it can be found out that everything is perfectly ok.
The tool is used to verify the system pre-requisites that are related to Oracle Clusterware, ASM and the databases.
There are few fix up scripts available if by any means the verification tool fails then these scripts can be used to automatically fix the errors.
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The backups should include OLR, OCR and ASM Metadata.
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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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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).
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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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When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC enviornment the same recovery for an instance is performed by the surviving nodes called Instance recovery.
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It is a private network which 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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One of the ways is to look at the database alert log for the time period when the database was started up.
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Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
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Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.
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The network ping failure is written in $CRS_HOME/log
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The ocrconfig -showbackup can be run to find out the automatic and manually run backups.
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You can use either the logical or the physical OCR backup copy to restore the Repository.
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You can use the dba_hist_seg_stats.
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The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.
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You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.
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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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All processing will show down to the CPU speed of the slowest server.
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Oracle Local repository contains information that allows the cluster processes to be started up with the OCR being in the ASM storage ssytem. Since the ASM file system is unavailable until the Grid processes are started up a local copy of the contents of the OCR is required which is stored in the OLR.
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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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You can use md_backup to restore the ASM diskgroup configuration in-case of ASM diskgroup storage loss.
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In 11g the following files can be stored in ASM diskgroups.
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This is the parameter which 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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A patch is considered a rolling if it is can be applied to the cluster binaries without having to shutting 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 instance open.
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Some of the RAC parameters are:
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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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The backups should include OLR, OCR and ASM Metadata.
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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Oracle RAC consists of a database that is represented in a clustered manner in the architecture. The cluster is the collection or pool of independent servers that make up one single system.
Cluster architecture provides more flexibility to manage and follow a modular incremental approach to improve the fault errors and provide an incremental system.
This architecture provides the maximum security in terms of ensuring high availability of the resources to the users.
It provides the resources on demand and provides hardware architecture such as failure at a single point is being removed.
The architecture provides the decoupling of the Oracle instance like the process and memory that are running on the server from the Oracle database.
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Oracle Real Application (RAC) provides the interaction of executable file with the Oracle database.
It allows the running of any packaged or custom built application with Oracle DB that is running on a server pool.It provides very high level of availability, flexibility and scalability to run the application and store it to the database.
It creates the database such that if the pool fails then the database is continued to run from the remaining servers and the load can be distributed.It makes it easier for the administrator to maintain many servers at the same time by load-balancing techniques and providing provision to add more and more servers when the load increases.
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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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A private N/W which 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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One of the ways is to look at the DB alert log for the time period when the DB was started up.
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Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
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Spfiles, ControlFiles, Datafiles and Redolog files should be created.
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The ocrconfig -showbackup can be run to find out the automatic and manually run backups.
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You can use either the logical or the physical OCR backup copy to restore the Repository.
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You can use the dba_hist_seg_stats.
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The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.
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You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.
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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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All processing will show down to the CPU speed of the slowest server.
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You can use md_backup to restore the ASM diskgroup configuration in-case of ASM diskgroup storage loss.
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In 11g the following files can be stored in ASM diskgroups.
In 12c the files below can also new be stored in the ASM Diskgroup
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This is the parameter which 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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A patch is considered a rolling if it is can be applied to the cluster binaries without having to shutting 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 instance open.
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Some of the RAC parameters are:
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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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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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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).
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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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Load balancing advisory is a process through which the load of the applications and resources can be managed throughout the servers.
It monitors the workload of the current activities from all the clusters and the instances that is being given on the server.
The service that is being provided is active all the time to see the workload of the applications on the servers.
To simplify it, it provides a percentage value to show the total workload of the instance and it flags the instance according to the quality.
Load Balancing Advisory helps in maintaining the loads from the servers and equally distributes it among many other servers that are not currently working.
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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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The backups should include OLR, OCR and ASM Metadata.
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