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.
Mention the Oracle RAC software components:-
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor
What are Oracle Clusterware processes for 10g on Unix and Linux
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
Cluster Ready Services (crsd) -- The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user
Event manager daemon (evmd) --A background process that publishes events that crs creates.
Process Monitor Daemon (OPROCD) --This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
RACG (racgmain, racgimon) --Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
What are Oracle database background processes specific to RAC
•LMS--Global Cache Service Process
•LMD--Global Enqueue Service Daemon
•LMON--Global Enqueue Service Monitor
•LCK0--Instance Enqueue Process
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.
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 do you troubleshoot node reboot ?
Please check metalink ...
Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.
How do you backup the OCR ?
There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\"clustername"\
To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore
With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup
How do you backup voting disk ?
#dd if=voting_disk_name of=backup_file_name
How do I identify the voting disk location ?
#crsctl query css votedisk
How do I identify the OCR file location ?
check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)
or
#ocrcheck
Is ssh required for normal Oracle RAC operation ?
"ssh" are not required for normal Oracle RAC operation. However "ssh" should be enabled for Oracle RAC and patchset installation.
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 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.
Why do we have a Virtual IP (VIP) in Oracle RAC ?
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.
What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report ?
This is most likely due to a fault in interconnect network.
Check netstat -s
if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.
How many nodes are supported in a RAC Database ?
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.
Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.
what is the purpose of the ONS daemon ?
The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners.
This in order to facilitate:
a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.
b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.
How do we find the location of OCR and voting disks ?
The location of OCR and Voting disks can be found as follows:
OCR location:
[oracle@dbcl1n1 AUCS1 ~]$ cat /etc/oracle/ocr.locO/P:
ocrconfig_loc=/export/ocw/oracle/ocr1
ocrmirrorconfig_loc=/export/ocw/oracle/ocr2
local_only=FALSE
Voting disk location:
[oracle@dbcl1n1 AUCS1 ~]$ cd $ORA_CRS_HOME/bin
[oracle@dbcl1n1 AUCS1 bin]$ ./crsctl query css votedisk
0. 0 /export/ocw/oracle/vote1
1. 0 /export/ocw/oracle/vote2
2. 0 /export/ocw/oracle/vote3
What is cache fusion ?
Ans :Cache fusion is the block shipping from one instance to another instance in a RAC environment.Due to Cache Fusion and the elimination of disk writes that occur when other instances request blocks for modifications, the performance overhead to manage shared data between instances is greatly diminished. Not only do Cache Fusion's concurrency controls greatly improve performance, but they also reduce the administrative effort for Real Application Clusters environments.
Cache Fusion addresses several types of concurrency as described under the following headings:
Concurrent Reads on Multiple Nodes
Concurrent Reads and Writes on Different Nodes
Concurrent Writes on Different Nodes
Which process is responsible for cache fusion mechanism ?
Global cache service(GCS)
A read request from an instance for a block that was modified by another instance and not yet written to disk can be a request for either the current version of the block or for a read-consistent version. In either case, the Global Cache Service Processes (LMSn) transfer the block from the holding instance's cache to the requesting instance's cache over the interconnect.
If we perform a DML acivity in a 2 node RAC environment,if that node disconnect due to some reason,What will be the result?
The DML statement will execute successfully since Database is there on the shared device.
Note: Thanks Junad for noticing the above answer and helping me in clarifying that in actual:
We neeed to write the callout functions using FAST APPLICATION NOTIFICATION (FAN) Notifications FOR RAC.The callout can be written in OCI, for example JAVA for dml failover to work.
http://download.oracle.com/docs/cd/B19306_01/rac.102/b14197/hafeats.htm
If you are using TAF (Transparent Application failover) with RAC Than only: session(alter session is not) failover,select failover,pre-connect and Basic Failover are supported.
http://download.oracle.com/docs/cd/B28359_01/network.111/b28316/advcfg.htm#NETAG338
http://www.scribd.com/doc/19211546/Failover-for-Rac
In Oracle 11g rel2:
http://www.oracle.com/technetwork/database/app-failover-oracle-database-11g-173323.pdf
How do we backup OCR and Voting disk?
VOTING DISK BACKUP:
To make a backup copy of the voting disk, use the Linux dd command. Perform this operation on every voting disk as needed where voting_disk_name is the name of the active voting disk and backup_file_name is the name of the file to which you want to back up the voting disk contents:
$dd if=voting_disk_name of=backup_file_name
If your voting disk is stored on a raw device, use the device name in place of voting_disk_name. For example:
dd if=/dev/sdd1 of=/tmp/voting.dmp
When you use the dd command for making backups of the voting disk, the backup can be performed while the Cluster Ready Services (CRS) process is active; you do not need to stop the crsd.bin process before taking a backup of the voting disk
OCR BACKUP:
Viewing Available OCR Backups
To find the most recent backup of the OCR, on any node in the cluster, use the following command:
$ocrconfig -showbackup
Backing Up the OCR
Because of the importance of OCR information, Oracle recommends that you use the ocrconfig tool to make copies of the automatically created backup files at least once a day.
In addition to using the automatically created OCR backup files, you should also export the OCR contents to a file before and after making significant configuration changes, such as adding or deleting nodes from your environment, modifying Oracle Clusterware resources, or creating a database. Exporting the OCR contents to a file lets you restore the OCR if your configuration changes cause errors. For example, if you have unresolvable configuration problems, or if you are unable to restart your cluster database after such changes, then you can restore your configuration by importing the saved OCR content from the valid configuration.
To export the contents of the OCR to a file, use the following command, where backup_file_name is the name of the OCR backup file you want to create:
$ocrconfig -exportbackup_file_name
What is global cache service,global enque service and global resource directory ?
Global Cache Service
GCS is the main controlling process that implements Cache Fusion. GCS tracks the location and the status (mode and role) of the data blocks, as well as the access privileges of various instances. GCS is the mechanism, which guarantees the data integrity by employing global access levels. GCS maintains the block modes for data blocks in the global role. It is also responsible for block transfers between the instances. Upon a request from an Instance GCS organizes the block shipping and appropriate lock mode conversions. The Global Cache Service is implemented by various background processes, such as the Global Cache Service Processes (LMSn) and Global Enqueue Service Daemon (LMD).
Global Enqueue Service
The Global Enqueue Service (GES) manages or tracks the status of all the Oracle enqueuing mechanisms. This involves all non Cache-fusion intra-instance operations. GES performs concurrency control on dictionary cache locks, library cache locks and the transactions. GES does this operation for resources that are accessed by more than one instance.
GES/GCS Areas
GES and GCS have the memory structures associated with global resources. It is distributed across all instances in a cluster. This area is located in the variable or shared pool section of the SGA. The list below shows the additions.
Global Resource Directory Global Resource Directory (GRD) is the internal database that records and stores the current status of the data blocks. Whenever a block is transferred out of a local cache to another instance’s cache, the GRD is updated. The following resources information is available in GRD.
* Data Block Identifiers (DBA)
* Location of most current version
* Modes of the data blocks ( (N)Null, (S)Shared, (X)Exclusive )
*The Roles of the data blocks (local or global) held by each instance
*Buffer caches on multiple nodes in the cluster
What is GRD ?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.
Give Details on Cache Fusion:-
Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion. Give Details on ACMS:-
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure.
Give details on GTX0-j :-
The process provides transparent support for XA global transactions in a RAC environment.The database autotunes the number of these processes based on the workload of XA global transactions.
Give details on LMON:-
This process monitors global enques and resources across the cluster and performs global enqueue recovery operations.This is called as Global Enqueue Service Monitor.
Give details on LMD:-
This process is called as global enqueue service daemon. This process manages incoming remote resource requests within each instance.
Give details on LMS:-
This process is called as Global Cache service process.This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature.
Give details on LCK0:-
This process is called as Instance enqueue process.This process manages non-cache fusion resource requests such as libry and row cache requests.
Give details on RMSn:-
This process is called as Oracle RAC management process.These pocesses perform managability tasks for Oracle RAC.Tasks include creation of resources related Oracle RAC when new instances are added to the cluster.
Give details on RSMN:-
This process is called as Remote Slave Monitor.This process manages background slave process creation andd communication on remote instances. This is a background slave process.This process performs tasks on behalf of a co-ordinating process running in another instance.
What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.
What is the significance of using cluster-aware shared storage in an Oracle RAC environment?
All instances of an Oracle RAC can access all the datafiles,control files, SPFILE's, redolog files when these files are hosted out of cluster-aware shared storage which are group of shared disks.
Give few examples for solutions that support cluster storage:-
ASM(automatic storage management),raw disk devices,network file system(NFS), OCFS2 and OCFS(Oracle Cluster Fie systems).
What is an interconnect network?
an interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.
How can we configure the cluster interconnect?
Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconnect.On unia and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol.
Can we use crossover cables with Oracle Clusterware interconnects?
No, crossover cables are not supported with Oracle Clusterware intercnects.
What is the use of cluster interconnect?
Cluster interconnect is used by the Cache fusion for inter instance communication.
How do users connect to database in an Oracle RAC environment?
Users can access a RAC database using a client/server configuration or through one or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database.
What is the use of a service in Oracle RAC environemnt?
Applications should use the services feature to connect to the Oracle database.Services enable us to define rules and characteristics to control how users and applications connect to database instances.
What are the characteriscs controlled by Oracle services feature?
The charateristics include a unique name, workload balancing and failover options,and high availability characteristics.
Which enable the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.
What is a virtual IP address or VIP?
A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.
What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.
Give situations under which VIP address failover happens:-
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.
What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.
What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using OEM(Enterprise Manager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA
How do we verify that RAC instances are running?
Issue the following query from any one node connecting through SQL*PLUS.
$connect sys/sys as sysdba
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.
What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.
Where can we apply FAN UP and DOWN events?
FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change?
During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.
Why should we have seperate homes for ASm instance?
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.
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 is rolling upgrade?
It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.
Can rolling upgrade be used to upgrade from 10g to 11g database?
No,it can be used only for Oracle database 11g releases(from 11.1).
State the initialization parameters that must have same value for every instance in an Oracle RAC database:-
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_PASSWORD_FILE
UNDO_MANAGEMENT
Can the DML_LOCKS and RESULT_CACHE_MAX_SIZE be identical on all instances?
These parameters can be identical on all instances only if these parameter values are set to zero.
What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set.
Mention the components of Oracle clusterware:-
Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR). What is a CRS resource?
Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc.
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).
How does a Oracle Clusterware manage CRS resources?
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).
Name some Oracle clusterware tools and their uses?
OIFCFG - allocating and deallocating network interfaces
OCRCONFIG - Command-line tool for managing Oracle Cluster Registry
OCRDUMP - Identify the interconnect being used
CVU - Cluster verification utility to get status of CRS resources
What are the modes of deleting instances from ORacle Real Application cluster Databases?
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).
How do we remove ASM from a Oracle RAC environment?
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows:
srvctl stop asm -n node_name
srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command:
srvctl config asm -n node_name
How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command:
srvctl config database -d database_name
cd CRS_HOME/bin
./crs_stat
How do we verify an existing current backup of OCR?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup
What are the performance views in an Oracle RAC environment?
We have v$ views that are instance specific. In addition we have GV$ views called as global views that has an INST_ID column of numeric data type.GV$ views obtain information from individual V$ views.
What are the types of connection load-balancing?
There are two types of connection load-balancing:server-side load balancing and client-side load balancing.
What is the differnece between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.
Give the usage of srvctl:-
srvctl start instance -d db_name -i "inst_name_list" [-o start_options]srvctl stop instance -d name -i "inst_name_list" [-o stop_options]srvctl stop instance -d orcl -i "orcl3,orcl4" -o immediatesrvctl start database -d name [-o start_options]srvctl stop database -d name [-o stop_options]srvctl start database -d orcl -o mount
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.
Mention the Oracle RAC software components:-
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor
What are Oracle Clusterware processes for 10g on Unix and Linux
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
Cluster Ready Services (crsd) -- The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user
Event manager daemon (evmd) --A background process that publishes events that crs creates.
Process Monitor Daemon (OPROCD) --This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
RACG (racgmain, racgimon) --Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
What are Oracle database background processes specific to RAC
•LMS--Global Cache Service Process
•LMD--Global Enqueue Service Daemon
•LMON--Global Enqueue Service Monitor
•LCK0--Instance Enqueue Process
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.
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 do you troubleshoot node reboot ?
Please check metalink ...
Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.
How do you backup the OCR ?
There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\"clustername"\
To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore
With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup
How do you backup voting disk ?
#dd if=voting_disk_name of=backup_file_name
How do I identify the voting disk location ?
#crsctl query css votedisk
How do I identify the OCR file location ?
check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)
or
#ocrcheck
Is ssh required for normal Oracle RAC operation ?
"ssh" are not required for normal Oracle RAC operation. However "ssh" should be enabled for Oracle RAC and patchset installation.
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 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.
Why do we have a Virtual IP (VIP) in Oracle RAC ?
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.
What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report ?
This is most likely due to a fault in interconnect network.
Check netstat -s
if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.
How many nodes are supported in a RAC Database ?
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.
Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.
what is the purpose of the ONS daemon ?
The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners.
This in order to facilitate:
a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.
b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.
How do we find the location of OCR and voting disks ?
The location of OCR and Voting disks can be found as follows:
OCR location:
[oracle@dbcl1n1 AUCS1 ~]$ cat /etc/oracle/ocr.locO/P:
ocrconfig_loc=/export/ocw/oracle/ocr1
ocrmirrorconfig_loc=/export/ocw/oracle/ocr2
local_only=FALSE
Voting disk location:
[oracle@dbcl1n1 AUCS1 ~]$ cd $ORA_CRS_HOME/bin
[oracle@dbcl1n1 AUCS1 bin]$ ./crsctl query css votedisk
0. 0 /export/ocw/oracle/vote1
1. 0 /export/ocw/oracle/vote2
2. 0 /export/ocw/oracle/vote3
What is cache fusion ?
Ans :Cache fusion is the block shipping from one instance to another instance in a RAC environment.Due to Cache Fusion and the elimination of disk writes that occur when other instances request blocks for modifications, the performance overhead to manage shared data between instances is greatly diminished. Not only do Cache Fusion's concurrency controls greatly improve performance, but they also reduce the administrative effort for Real Application Clusters environments.
Cache Fusion addresses several types of concurrency as described under the following headings:
Concurrent Reads on Multiple Nodes
Concurrent Reads and Writes on Different Nodes
Concurrent Writes on Different Nodes
Which process is responsible for cache fusion mechanism ?
Global cache service(GCS)
A read request from an instance for a block that was modified by another instance and not yet written to disk can be a request for either the current version of the block or for a read-consistent version. In either case, the Global Cache Service Processes (LMSn) transfer the block from the holding instance's cache to the requesting instance's cache over the interconnect.
If we perform a DML acivity in a 2 node RAC environment,if that node disconnect due to some reason,What will be the result?
The DML statement will execute successfully since Database is there on the shared device.
Note: Thanks Junad for noticing the above answer and helping me in clarifying that in actual:
We neeed to write the callout functions using FAST APPLICATION NOTIFICATION (FAN) Notifications FOR RAC.The callout can be written in OCI, for example JAVA for dml failover to work.
http://download.oracle.com/docs/cd/B19306_01/rac.102/b14197/hafeats.htm
If you are using TAF (Transparent Application failover) with RAC Than only: session(alter session is not) failover,select failover,pre-connect and Basic Failover are supported.
http://download.oracle.com/docs/cd/B28359_01/network.111/b28316/advcfg.htm#NETAG338
http://www.scribd.com/doc/19211546/Failover-for-Rac
In Oracle 11g rel2:
http://www.oracle.com/technetwork/database/app-failover-oracle-database-11g-173323.pdf
How do we backup OCR and Voting disk?
VOTING DISK BACKUP:
To make a backup copy of the voting disk, use the Linux dd command. Perform this operation on every voting disk as needed where voting_disk_name is the name of the active voting disk and backup_file_name is the name of the file to which you want to back up the voting disk contents:
$dd if=voting_disk_name of=backup_file_name
If your voting disk is stored on a raw device, use the device name in place of voting_disk_name. For example:
dd if=/dev/sdd1 of=/tmp/voting.dmp
When you use the dd command for making backups of the voting disk, the backup can be performed while the Cluster Ready Services (CRS) process is active; you do not need to stop the crsd.bin process before taking a backup of the voting disk
OCR BACKUP:
Viewing Available OCR Backups
To find the most recent backup of the OCR, on any node in the cluster, use the following command:
$ocrconfig -showbackup
Backing Up the OCR
Because of the importance of OCR information, Oracle recommends that you use the ocrconfig tool to make copies of the automatically created backup files at least once a day.
In addition to using the automatically created OCR backup files, you should also export the OCR contents to a file before and after making significant configuration changes, such as adding or deleting nodes from your environment, modifying Oracle Clusterware resources, or creating a database. Exporting the OCR contents to a file lets you restore the OCR if your configuration changes cause errors. For example, if you have unresolvable configuration problems, or if you are unable to restart your cluster database after such changes, then you can restore your configuration by importing the saved OCR content from the valid configuration.
To export the contents of the OCR to a file, use the following command, where backup_file_name is the name of the OCR backup file you want to create:
$ocrconfig -exportbackup_file_name
What is global cache service,global enque service and global resource directory ?
Global Cache Service
GCS is the main controlling process that implements Cache Fusion. GCS tracks the location and the status (mode and role) of the data blocks, as well as the access privileges of various instances. GCS is the mechanism, which guarantees the data integrity by employing global access levels. GCS maintains the block modes for data blocks in the global role. It is also responsible for block transfers between the instances. Upon a request from an Instance GCS organizes the block shipping and appropriate lock mode conversions. The Global Cache Service is implemented by various background processes, such as the Global Cache Service Processes (LMSn) and Global Enqueue Service Daemon (LMD).
Global Enqueue Service
The Global Enqueue Service (GES) manages or tracks the status of all the Oracle enqueuing mechanisms. This involves all non Cache-fusion intra-instance operations. GES performs concurrency control on dictionary cache locks, library cache locks and the transactions. GES does this operation for resources that are accessed by more than one instance.
GES/GCS Areas
GES and GCS have the memory structures associated with global resources. It is distributed across all instances in a cluster. This area is located in the variable or shared pool section of the SGA. The list below shows the additions.
Global Resource Directory Global Resource Directory (GRD) is the internal database that records and stores the current status of the data blocks. Whenever a block is transferred out of a local cache to another instance’s cache, the GRD is updated. The following resources information is available in GRD.
* Data Block Identifiers (DBA)
* Location of most current version
* Modes of the data blocks ( (N)Null, (S)Shared, (X)Exclusive )
*The Roles of the data blocks (local or global) held by each instance
*Buffer caches on multiple nodes in the cluster
What is GRD ?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.
Give Details on Cache Fusion:-
Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion. Give Details on ACMS:-
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure.
Give details on GTX0-j :-
The process provides transparent support for XA global transactions in a RAC environment.The database autotunes the number of these processes based on the workload of XA global transactions.
Give details on LMON:-
This process monitors global enques and resources across the cluster and performs global enqueue recovery operations.This is called as Global Enqueue Service Monitor.
Give details on LMD:-
This process is called as global enqueue service daemon. This process manages incoming remote resource requests within each instance.
Give details on LMS:-
This process is called as Global Cache service process.This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature.
Give details on LCK0:-
This process is called as Instance enqueue process.This process manages non-cache fusion resource requests such as libry and row cache requests.
Give details on RMSn:-
This process is called as Oracle RAC management process.These pocesses perform managability tasks for Oracle RAC.Tasks include creation of resources related Oracle RAC when new instances are added to the cluster.
Give details on RSMN:-
This process is called as Remote Slave Monitor.This process manages background slave process creation andd communication on remote instances. This is a background slave process.This process performs tasks on behalf of a co-ordinating process running in another instance.
What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.
What is the significance of using cluster-aware shared storage in an Oracle RAC environment?
All instances of an Oracle RAC can access all the datafiles,control files, SPFILE's, redolog files when these files are hosted out of cluster-aware shared storage which are group of shared disks.
Give few examples for solutions that support cluster storage:-
ASM(automatic storage management),raw disk devices,network file system(NFS), OCFS2 and OCFS(Oracle Cluster Fie systems).
What is an interconnect network?
an interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.
How can we configure the cluster interconnect?
Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconnect.On unia and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol.
Can we use crossover cables with Oracle Clusterware interconnects?
No, crossover cables are not supported with Oracle Clusterware intercnects.
What is the use of cluster interconnect?
Cluster interconnect is used by the Cache fusion for inter instance communication.
How do users connect to database in an Oracle RAC environment?
Users can access a RAC database using a client/server configuration or through one or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database.
What is the use of a service in Oracle RAC environemnt?
Applications should use the services feature to connect to the Oracle database.Services enable us to define rules and characteristics to control how users and applications connect to database instances.
What are the characteriscs controlled by Oracle services feature?
The charateristics include a unique name, workload balancing and failover options,and high availability characteristics.
Which enable the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.
What is a virtual IP address or VIP?
A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.
What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.
Give situations under which VIP address failover happens:-
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.
What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.
What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using OEM(Enterprise Manager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA
How do we verify that RAC instances are running?
Issue the following query from any one node connecting through SQL*PLUS.
$connect sys/sys as sysdba
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.
What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.
Where can we apply FAN UP and DOWN events?
FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change?
During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.
Why should we have seperate homes for ASm instance?
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.
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 is rolling upgrade?
It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.
Can rolling upgrade be used to upgrade from 10g to 11g database?
No,it can be used only for Oracle database 11g releases(from 11.1).
State the initialization parameters that must have same value for every instance in an Oracle RAC database:-
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_PASSWORD_FILE
UNDO_MANAGEMENT
Can the DML_LOCKS and RESULT_CACHE_MAX_SIZE be identical on all instances?
These parameters can be identical on all instances only if these parameter values are set to zero.
What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set.
Mention the components of Oracle clusterware:-
Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR). What is a CRS resource?
Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc.
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).
How does a Oracle Clusterware manage CRS resources?
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).
Name some Oracle clusterware tools and their uses?
OIFCFG - allocating and deallocating network interfaces
OCRCONFIG - Command-line tool for managing Oracle Cluster Registry
OCRDUMP - Identify the interconnect being used
CVU - Cluster verification utility to get status of CRS resources
What are the modes of deleting instances from ORacle Real Application cluster Databases?
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).
How do we remove ASM from a Oracle RAC environment?
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows:
srvctl stop asm -n node_name
srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command:
srvctl config asm -n node_name
How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command:
srvctl config database -d database_name
cd CRS_HOME/bin
./crs_stat
How do we verify an existing current backup of OCR?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup
What are the performance views in an Oracle RAC environment?
We have v$ views that are instance specific. In addition we have GV$ views called as global views that has an INST_ID column of numeric data type.GV$ views obtain information from individual V$ views.
What are the types of connection load-balancing?
There are two types of connection load-balancing:server-side load balancing and client-side load balancing.
What is the differnece between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.
Give the usage of srvctl:-
srvctl start instance -d db_name -i "inst_name_list" [-o start_options]srvctl stop instance -d name -i "inst_name_list" [-o stop_options]srvctl stop instance -d orcl -i "orcl3,orcl4" -o immediatesrvctl start database -d name [-o start_options]srvctl stop database -d name [-o stop_options]srvctl start database -d orcl -o mount
