RAC Architecture
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Transcript of RAC Architecture
RAC Architecture
Oracle Real Application clusters allows multiple instances to access a single database, the instances will be running on multiple nodes. In an standard Oracle configuration a database can only be mounted by one instance but in a RAC environment many instances can access a single database.
Oracle's RAC is heavy dependent on a efficient, high reliable high speed private network called the interconnect, make sure when designing a RAC system that you get the best that you can afford.
The table below describes the difference of a standard oracle database (single instance) an a RAC environment
Component Single Instance Environment RAC Environment
SGA Instance has its own SGA Each instance has its own SGA
Background processes
Instance has its own set of background processes
Each instance has its own set of background processes
Datafiles Accessed by only one instance Shared by all instances (shared storage)
Control Files Accessed by only one instance Shared by all instances (shared storage)
Online Redo Logfile Dedicated for write/read to only one instance
Only one instance can write but other instances can read during recovery and archiving. If an instance is shutdown, log switches by other instances can force the idle instance redo logs to be archived
Archived Redo Logfile
Dedicated to the instance Private to the instance but other instances will need access to all required archive logs during media recovery
Flash Recovery Log Accessed by only one instance Shared by all instances (shared storage)
Alert Log and Trace Files
Dedicated to the instance Private to each instance, other instances never read or write to those files.
ORACLE_HOMEMultiple instances on the same server accessing different databases ca use the same executable files
Same as single instance plus can be placed on shared file system allowing a common ORACLE_HOME for all instances in a RAC environment.
RAC Components
The major components of a Oracle RAC system are
Shared disk system Oracle Clusterware
Cluster Interconnects
Oracle Kernel Components
The below diagram describes the basic architecture of the Oracle RAC environment
Here are a list of processes running on a freshly installed RAC
Disk architecture
With today's SAN and NAS disk storage systems, sharing storage is fairly easy and is required for a RAC environment, you can use the below storage setups
SAN (Storage Area Networks) - generally using fibre to connect to the SAN NAS ( Network Attached Storage) - generally using a network to connect to the NAS using either NFS, ISCSI
JBOD - direct attached storage, the old traditional way and still used by many companies as a cheap option
All of the above solutions can offer multi-pathing to reduce SPOFs within the RAC environment, there is no reason not to configure multi-pathing as the cost is cheap when adding additional paths to the disk because most of the expense is paid when out when configuring the first path, so an additional controller card and network/fibre cables is all that is need.
The last thing to think about is how to setup the underlining disk structure this is known as a raid level, there are about 12 different raid levels that I know off, here are the most common ones
raid 0 (Striping)
A number of disks are concatenated together to give the appearance of one very large disk.
Advantages Improved performance Can Create very large Volumes
Disadvantages Not highly available (if one disk fails, the volume fails)
raid 1 (Mirroring)
A single disk is mirrored by another disk, if one disk fails the system is unaffected as it can use its mirror.
Advantages Improved performance Highly Available (if one disk fails the mirror takes over)
Disadvantages Expensive (requires double the number of disks)
raid 5
Raid stands for Redundant Array of Inexpensive Disks, the disks are striped with parity across 3 or more disks, the parity is used in the event that one of the disks fails, the data on the failed disk is reconstructed by using the parity bit.
Advantages Improved performance (read only) Not expensive
Disadvantages Slow write operations (caused by having to create the parity bit)
There are many other raid levels that can be used with a particular hardware environment for example EMC storage uses the RAID-S, HP storage uses Auto RAID, so check with the manufacture for the best solution that will provide you with the best performance and resilience.
Once you have you storage attached to the servers, you have three choices on how to setup the disks
Raw Volumes - normally used for performance benefits, however they are hard to manage and backup Cluster FileSystem - used to hold all the Oracle datafiles can be used by windows and linux, its not used widely
Automatic Storage Management (ASM) - Oracle choice of storage management, its a portable, dedicated and optimized cluster filesystem
I will only be discussing ASM, which i have already have a topic on called Automatic Storage Management.
Oracle Clusterware
Oracle Clusterware software is designed to run Oracle in a cluster mode, it can support you to 64 nodes, it can even be used with a vendor cluster like Sun Cluster.
The Clusterware software allows nodes to communicate with each other and forms the cluster that makes the nodes work as a single logical server. The software is run by the Cluster Ready Services (CRS) using the Oracle Cluster Registry (OCR) that records and maintains the cluster and node membership information and the voting disk which acts as a tiebreaker during communication failures. Consistent heartbeat information travels across the interconnect to the voting disk when the cluster is running.
The CRS has four components
OPROCd - Process Monitor Daemon CRSd - CRS daemon, the failure of this daemon results in a node being reboot to avoid data corruption
OCSSd - Oracle Cluster Synchronization Service Daemon (updates the registry)
EVMd - Event Volume Manager Daemon
The OPROCd daemon provides the I/O fencing for the Oracle cluster, it uses the hangcheck timer or watchdog timer for the cluster integrity. It is locked into memory and runs as a realtime processes, failure of this daemon results in the node being rebooted. Fencing is used to protect the data, if a node were to have problems fencing presumes the worst and protects the data thus restarts the node in question, its better to be save than sorry.
The CRSd process manages resources such as starting and stopping the services and failover of the application resources, it also spawns separate processes to manage application resources. CRS manages the OCR and stores the current know state of the cluster, it
requires a public, private and VIP interface in order to run. OCSSd provides synchronization services among nodes, it provides access to the node membership and enables basic cluster services, including cluster group services and locking, failure of this daemon causes the node to be rebooted to avoid split-brain situations.
The below functions are covered by the OCSSd
CSS provides basic Group Services Support, it is a distributed group membership system that allows applications to coordinate activities to archive a common result.
Group services use vendor clusterware group services when it is available.
Lock services provide the basic cluster-wide serialization locking functions, it uses the First In, First Out (FIFO) mechanism to manage locking
Node services uses OCR to store data and updates the information during reconfiguration, it also manages the OCR data which is static otherwise.
The last component is the Event Management Logger, which runs the EVMd process. The daemon spawns a processes called evmlogger and generates the events when things happen. The evmlogger spawns new children processes on demand and scans the callout directory to invoke callouts. Death of the EVMd daemon will not halt the instance and will be restarted.
Quick recap
CRS Process Functionality Failure of the Process Run AS
OPROCd - Process Monitor provides basic cluster integrity services Node Restart root
EVMd - Event Management spawns a child process event logger and generates callouts
Daemon automatically restarted, no node restart
oracle
OCSSd - Cluster Synchronization Services
basic node membership, group services, basic locking
Node Restart oracle
CRSd - Cluster Ready Services resource monitoring, failover and node recovery
Daemon restarted automatically, no node restart
root
The cluster-ready services (CRS) is a new component in 10g RAC, its is installed in a separate home directory called ORACLE_CRS_HOME. It is a mandatory component but can be used with a third party cluster (Veritas, Sun Cluster), by default it manages the node membership functionality along with managing regular RAC-related resources and services
RAC uses a membership scheme, thus any node wanting to join the cluster as to become a member. RAC can evict any member that it seems as a problem, its primary concern is protecting the data. You can add and remove nodes from the cluster and the membership increases or decrease, when network problems occur membership becomes the deciding factor on which part stays as the cluster and what nodes get evicted, the use of a voting disk is used which I will talk about later.
The resource management framework manage the resources to the cluster (disks, volumes), thus you can have only have one resource management framework per resource. Multiple frameworks are not supported as it can lead to undesirable affects.
The Oracle Cluster Ready Services (CRS) uses the registry to keep the cluster configuration, it should reside on a shared storage and accessible to all nodes within the cluster. This shared storage is known as the Oracle Cluster Registry (OCR) and its a major part of the cluster, it is automatically backed up (every 4 hours) the daemons plus you can manually back it up. The OCSSd uses the OCR extensively and writes the changes to the registry
The OCR keeps details of all resources and services, it stores name and value pairs of information such as resources that are used to manage the resource equivalents by the CRS stack. Resources with the CRS stack are components that are managed by CRS and have the information on the good/bad state and the callout scripts. The OCR is also used to supply bootstrap information ports, nodes, etc, it is a binary file.
The OCR is loaded as cache on each node, each node will update the cache then only one node is allowed to write the cache to the OCR file, the node is called the master. The Enterprise manager also uses the OCR cache, it should be at least 100MB in size. The CRS daemon will update the OCR about status of the nodes in the cluster during reconfigurations and failures.
The voting disk (or quorum disk) is shared by all nodes within the cluster, information about the cluster is constantly being written to the disk, this is know as the heartbeat. If for any reason a node cannot access the voting disk it is immediately evicted from the cluster, this protects the cluster from split-brains (the Instance Membership Recovery algorithm IMR is used to detect and resolve split-brains) as the voting disk decides what part is the really cluster. The voting disk manages the cluster membership and arbitrates the cluster ownership during communication failures between nodes. Voting is often confused with quorum the are similar but distinct, below details what each means
Voting A vote is usually a formal expression of opinion or will in response to a proposed decision
Quorumis defined as the number, usually a majority of members of a body, that, when assembled is legally competent to transact business
The only vote that counts is the quorum member vote, the quorum member vote defines the cluster. If a node or group of nodes cannot archive a quorum, they should not start any services because they risk conflicting with an established quorum.
The voting disk has to reside on shared storage, it is a a small file (20MB) that can be accessed by all nodes in the cluster. In Oracle 10g R1 you can have only one voting disk, but in R2 you can have upto 32 voting disks allowing you to eliminate any SPOF's.
The original Virtual IP in Oracle was Transparent Application Failover (TAF), this had limitations, this has now been replaced with cluster VIPs. The cluster VIPs will failover to working nodes if a node should fail, these public IPs are configured in DNS so that users can access them. The cluster VIPs are different from the cluster interconnect IP address and are only used to access the database.
The cluster interconnect is used to synchronize the resources of the RAC cluster, and also used to transfer some data from one instance to another. This interconnect should be private, highly available and fast with low latency, ideally they should be on a minimum private 1GB network. What ever hardware you are using the NIC should use multi-pathing (Linux - bonding, Solaris - IPMP). You can use crossover cables in a QA/DEV environment but it is not supported in a production environment, also crossover cables limit you to a two node cluster.
Oracle Kernel Components
The kernel components relate to the background processes, buffer cache and shared pool and managing the resources without conflicts and corruptions requires special handling.
In RAC as more than one instance is accessing the resource, the instances require better coordination at the resource management level. Each node will have its own set of buffers but will be able to request and receive data blocks currently held in another instance's cache. The management of data sharing and exchange is done by the Global Cache Services (GCS).
All the resources in the cluster group form a central repository called the Global Resource Directory (GRD), which is distributed. Each instance masters some set of resources and together all instances form the GRD. The resources are equally distributed among the nodes based on their weight. The GRD is managed by two services called Global Caches Services (GCS) and Global Enqueue Services (GES), together they form and manage the GRD. When a node leaves the cluster, the GRD portion of that instance needs to be redistributed to the surviving nodes, a similar action is performed when a new node joins.
RAC Background Processes
Each node has its own background processes and memory structures, there are additional processes than the norm to manage the shared resources, theses additional processes maintain cache coherency across the nodes.
Cache coherency is the technique of keeping multiple copies of a buffer consistent between different Oracle instances on different nodes. Global cache management ensures that access to a master copy of a data block in one buffer cache is coordinated with the copy of the block in another buffer cache.
The sequence of a operation would go as below
1. When instance A needs a block of data to modify, it reads the bock from disk, before reading it must inform the GCS (DLM). GCS keeps track of the lock status of the data block by keeping an exclusive lock on it on behalf of instance A
2. Now instance B wants to modify that same data block, it to must inform GCS, GCS will then request instance A to release the lock, thus GCS ensures that instance B gets the latest version of the data block (including instance A modifications) and then exclusively locks it on instance B behalf.
3. At any one point in time, only one instance has the current copy of the block, thus keeping the integrity of the block.
GCS maintains data coherency and coordination by keeping track of all lock status of each block that can be read/written to by any nodes in the RAC. GCS is an in memory database that contains information about current locks on blocks and instances waiting to acquire locks. This is known as Parallel Cache Management (PCM). The Global Resource Manager (GRM) helps to coordinate and communicate the lock requests from Oracle processes between instances in the RAC. Each instance has a buffer cache in its SGA, to ensure that each RAC instance obtains the block that it needs to satisfy a query or transaction. RAC uses two processes the GCS and GES which maintain records of lock status of each data file and each cached block using a GRD.
So what is a resource, it is an identifiable entity, it basically has a name or a reference, it can be a area in memory, a disk file or an abstract entity. A resource can be owned or locked in various states (exclusive or shared). Any shared resource is lockable and if it is not shared no access conflict will occur.
A global resource is a resource that is visible to all the nodes within the cluster. Data buffer cache blocks are the most obvious and most heavily global resource, transaction enqueue's and database data structures are other examples. GCS handle data buffer cache blocks and GES handle all the non-data block resources.
All caches in the SGA are either global or local, dictionary and buffer caches are global, large and java pool buffer caches are local. Cache fusion is used to read the data buffer cache from another instance instead of getting the block from disk, thus cache fusion moves current copies of data blocks between instances (hence why you need a fast private network), GCS manages the block transfers between the instances.
Finally we get to the processes
Oracle RAC Daemons and Processes
LMSnLock Manager Server process - GCS
this is the cache fusion part and the most active process, it handles the consistent copies of blocks that are transferred between instances. It receives requests from LMD to perform lock requests. I rolls back any uncommitted transactions. There can be up to ten LMS processes running and can be started dynamically if demand requires it.
they manage lock manager service requests for GCS resources and send them to a service queue to be handled by the LMSn process. It also handles global deadlock detection and monitors for lock conversion timeouts.
as a performance gain you can increase this process priority to make sure CPU starvation does not occur
you can see the statistics of this daemon by looking at the view X$KJMSDP
LMONLock Monitor Process - GES
this process manages the GES, it maintains consistency of GCS memory structure in case of process death. It is also responsible for cluster reconfiguration and locks reconfiguration (node joining or leaving), it checks for instance deaths and listens for local messaging.
A detailed log file is created that tracks any reconfigurations that have happened.
LMDLock Manager Daemon - GES
this manages the enqueue manager service requests for the GCS. It also handles deadlock detention and remote resource requests from other instances.
you can see the statistics of this daemon by looking at the view X$KJMDDP
LCK0Lock Process - GES
manages instance resource requests and cross-instance call operations for shared resources. It builds a list of invalid lock elements and validates lock elements during recovery.
DIAG Diagnostic This is a lightweight process, it uses the DIAG framework to monitor the health of the cluster. It captures
Daemon information for later diagnosis in the event of failures. It will perform any necessary recovery if an operational hang is detected.
RAC Administration
I am only going to talk about RAC administration, if you need Oracle administration then see my Oracle section.
It is recommended that the spfile (binary parameter file) is shared between all nodes within the cluster, but it is possible that each instance can have its own spfile. The parameters can be grouped into three categories
Unique parameters These parameters are unique to each instance, examples would be instance_name, thread and undo_tablespace
Identical parameters Parameters in this category must be the same for each instance, examples would be db_name and control_file
Neither unique or identical parameters
parameters that are not in any of the above, examples would be db_cache_size, large_pool_size, local_listener and gcs_servers_processes
The main unique parameters that you should know about are
instance_name - defines the name of the Oracle instance (default is the value of the oracle_sid variable) instance_number - a unique number for each instance must be greater than 0 but smaller than the max_instance parameter
thread - specifies the set of redolog files to be used by the instance
undo_tablespace - specifies the name of the undo tablespace to be used by the instance
rollback_segments - you should use Automatic Undo Management
cluster_interconnects - use if only if Oracle has trouble not picking the correct interconnects
The identical unique parameters that you should know about are below you can use the below query to view all of them
select name, isinstance_modifiable from v$parameter where isinstance_modifiable = 'false' order by name;
cluster_database - options are true or false, mounts the control file in either share (cluster) or exclusive mode, use false in the below cases
o Converting from no archive log mode to archive log mode and vice versa
o Enabling the flashback database feature
o Performing a media recovery on a system table
o Maintenance of a node
active_instance_count - used for primary/secondary RAC environments
cluster_database_instances - specifies the number of instances that will be accessing the database (set to maximum # of nodes)
dml_locks - specifies the number of DML locks for a particular instance (only change if you get ORA-00055 errors)
gc_files_to_locks - specify the number of global locks to a data file, changing this disables the Cache Fusion.
max_commit_propagation_delay - influences the mechanism Oracle uses to synchronize the SCN among all instances
instance_groups - specify multiple parallel query execution groups and assigns the current instance to those groups
parallel_instance_group - specifies the group of instances to be used for parallel query execution
gcs_server_processes - specify the number of lock manager server (LMS) background processes used by the instance for Cache Fusion
remote_listener - register the instance with listeners on remote nodes.
syntax for parameter file
<instance_name>.<parameter_name>=<parameter_value>
inst1.db_cache_size = 1000000*.undo_management=auto
examplealter system set db_2k_cache_size=10m scope=spfile sid='inst1';
Note: use the sid option to specify a particular instance
Starting and Stopping Instances
The srvctl command is used to start/stop an instance, you can also use sqlplus to start and stop the instance
start all instances
srvctl start database -d <database> -o <option>
Note: starts listeners if not already running, you can use the -o option to specify startup/shutdown options, see below for options
forceopenmountnomount
stop all instances
srvctl stop database -d <database> -o <option>
Note: the listeners are not stopped, you can use the -o option to specify startup/shutdown options, see below for options
immediateabort normaltransactional
start/stop particular instance
srvctl [start|stop] database -d <database> -i <instance>,<instance>
Undo Management
To recap on undo management you can see my undo section, instances in a RAC do not share undo, they each have a dedicated undo tablespace. Using the undo_tablespace parameter each instance can point to its own undo tablespace
undo tablespace instance1.undo_tablespace=undo_tbs1instance2.undo_tablespace=undo_tbs2
With todays Oracle you should be using automatic undo management, again I have a detailed discussion on AUM in my undo section.
Temporary Tablespace
I have already discussed temporary tablespace's, in a RAC environment you should setup a temporary tablespace group, this group is then used by all instances of the RAC. Each instance creates a temporary segment in the temporary tablespace it is using. If an instance is running a large sort, temporary segments can be reclaimed from segments from other instances in that tablespace.
useful views
gv$sort_segment - explore current and maximum sort segment usage statistics (check columns freed_extents, free_requests ,if they grow increase tablespace size) gv$tempseg_usage - explore temporary segment usage details such as name, SQL, etc v$tempfile - identify - temporary datafiles being used for the temporary tablespace
Redologs
I have already discussed redologs, in a RAC environment every instance has its own set of redologs. Each instance has exclusive write access to its own redologs, but each instance can read each others redologs, this is used for recovery. Redologs are located on the shared storage so that all instances can have access to each others redologs. The process is a little different to the standard Oracle when changing the archive mode
archive mode (RAC) SQL> alter system set cluster_database=false scope=spfile sid='prod1';srvctl stop database -d <database>SQL> startup mountSQL> alter database archivelog;
SQL> alter system set cluster_database=true scope=spfile sid='prod1';SQL> shutdown;srvctl start database -d prod
Flashback
Again I have already talked about flashback, there is no difference in RAC environment apart from the setting up
flashback (RAC)
## Make sure that the database is running in archive log mode SQL> archive log list
## Setup the flashbackSQL> alter system set cluster_database=false scope=spfile sid='prod1';SQL> alter system set DB_RECOVERY_FILE_DEST_SIZE=200M scope=spfile;SQL> alter system set DB_RECOVERY_FILE_DEST='/ocfs2/flashback' scope=spfile;srvctl stop database -p prod1SQL> startup mountSQL> alter database flashback on;SQL> shutdown;srvctl start database -p prod1
SRVCTL command
We have already come across the srvctl above, this command is called the server control utility. It can divided into two categories
Database configuration tasks Database instance control tasks
Oracle stores database configuration in a repository, the configuration is stored in the Oracle Cluster Registry (OCR) that was created when RAC was installed, it will be located on the shared storage. Srvctl uses CRS to communicate and perform startup and shutdown commands on other nodes.
I suggest that you lookup the command but I will provide a few examples
display the registered databases
srvctl config database
status
srvctl status database -d <databasesrvctl status instance -d <database> -i <instance> srvctl status nodeapps -n <node>srvctl status service -d <database> srvctl status asm -n <node>
stopping/starting
srvctl stop database -d <database>srvctl stop instance -d <database> -i <instance>,<instance>srvctl stop service -d <database> [-s <service><service>] [-i <instance>,<instance>]srvctl stop nodeapps -n <node>srvctl stop asm -n <node>
srvctl start database -d <database>srvctl start instance -d <database> -i <instance>,<instance>srvctl start service -d <database> -s <service><service> -i <instance>,<instance>srvctl start nodeapps -n <node>srvctl start asm -n <node>
adding/removing
srvctl add database -d <database> -o <oracle_home>srvctl add instance -d <database> -i <instance> -n <node>srvctl add service -d <database> -s <service> -r <preferred_list>srvctl add nodeapps -n <node> -o <oracle_home> -A <name|ip>/networksrvctl add asm -n <node> -i <asm_instance> -o <oracle_home>
srvctl remove database -d <database> -o <oracle_home>srvctl remove instance -d <database> -i <instance> -n <node>srvctl remove service -d <database> -s <service> -r <preferred_list>srvctl remove nodeapps -n <node> -o <oracle_home> -A <name|ip>/networksrvctl asm remove -n <node>
Services
Services are used to manage the workload in Oracle RAC, the important features of services are
used to distribute the workload can be configured to provide high availability
provide a transparent way to direct workload
The view v$services contains information about services that have been started on that instance, here is a list from a fresh RAC installation
The table above is described below
Goal - allows you to define a service goal using service time, throughput or none Connect Time Load Balancing Goal - listeners and mid-tier servers contain current information about service performance
Distributed Transaction Processing - used for distributed transactions
AQ_HA_Notifications - information about nodes being up or down will be sent to mid-tier servers via the advance queuing mechanism
Preferred and Available Instances - the preferred instances for a service, available ones are the backup instances
You can administer services using the following tools
DBCA
EM (Enterprise Manager)
DBMS_SERVICES
Server Control (srvctl)
Two services are created when the database is first installed, these services are running all the time and cannot be disabled.
sys$background - used by an instance's background processes only sys$users - when users connect to the database without specifying a service they use this service
add
srvctl add service -d D01 -s BATCH_SERVICE -r node1,node2 -a node3
Note: the options are describe below
-d - database-s - the service-r - the service will running on the these nodes-a - if nodes in the -r list are not running then run on this node
remove srvctl remove service -d D01 -s BATCH_SERVICE
start srvctl start service -d D01 -s BATCH_SERVICE
stop srvctl stop service -d D01 -s BATCH_SERVICE
status srvctl status service -d D10 -s BATCH_SERVICE
service (example) ## create the JOB class BEGIN DBMS_SCHEDULER.create_job_class( job_class_name => 'BATCH_JOB_CLASS', service => 'BATCH_SERVICE');END;/
## Grant the privileges to execute the job
grant execute on sys.batch_job_class to vallep;
## create a job associated with a job class BEGIN DBMS_SCHDULER.create_job( job_name => 'my_user.batch_job_test', job_type => 'PLSQL_BLOCK', job_action => SYSTIMESTAMP' repeat_interval => 'FREQ=DAILY;', job_class => 'SYS.BATCH_JOB_CLASS', end_date => NULL, enabled => TRUE, comments => 'Test batch job to show RAC services');END;/
## assign a job class to an existing job exec dbms_scheduler.set_attribute('MY_BATCH_JOB', 'JOB_CLASS', 'BATCH_JOB_CLASS');
Cluster Ready Services (CRS)
CRS is Oracle's clusterware software, you can use it with other third-party clusterware software, though it is not required (apart from HP True64).
CRS is start automatically when the server starts, you should only stop this service in the following situations
Applying a patch set to $ORA_CRS_HOME O/S maintenance
Debugging CRS problems
CRS Administration
starting
## Starting CRS using Oracle 10g R1not possible
## Starting CRS using Oracle 10g R2$ORA_CRS_HOME/bin/crsctl start crs
stopping
## Stopping CRS using Oracle 10g R1 srvctl stop -d database <database>srvctl stop asm -n <node>srvctl stop nodeapps -n <node>/etc/init.d/init.crs stop
## Stopping CRS using Oracle 10g R2 $ORA_CRS_HOME/bin/crsctl stop crs
disabling/enabling
## stop CRS restarting after a reboot, basically permanent over reboots
## Oracle 10g R1 /etc/init.d/init.crs [disable|enable]
## Oracle 10g R2$ORA_CRS_HOME/bin/crsctl [disable|enable] crs
checking
$ORA_CRS_HOME/bin/crsctl check crs$ORA_CRS_HOME/bin/crsctl check evmd$ORA_CRS_HOME/bin/crsctl check cssd$ORA_CRS_HOME/bin/crsctl check crsd$ORA_CRS_HOME/bin/crsctl check install -wait 600
Resource Applications (CRS Utilities)
status $ORA_CRS_HOME/bin/crs_stat$ORA_CRS_HOME/bin/crs_stat -t $ORA_CRS_HOME/bin/crs_stat -ls $ORA_CRS_HOME/bin/crs_stat -p
Note:-t more readable display -ls permission listing-p parameters
create profile $ORA_CRS_HOME/bin/crs_profile
register/unregister application $ORA_CRS_HOME/bin/crs_register$ORA_CRS_HOME/bin/crs_unregister
Start/Stop an application $ORA_CRS_HOME/bin/crs_start$ORA_CRS_HOME/bin/crs_stop
Resource permissions $ORA_CRS_HOME/bin/crs_getparam$ORA_CRS_HOME/bin/crs_setparam
Relocate a resource $ORA_CRS_HOME/bin/crs_relocate
Nodes
member number/name olsnodes -n
Note: the olsnodes command is located in $ORA_CRS_HOME/bin
local node name olsnodes -l
activates logging olsnodes -g
Oracle Interfaces
display oifcfg getif
delete oicfg delig -global
setoicfg setif -global <interface name>/<subnet>:publicoicfg setif -global <interface name>/<subnet>:cluster_interconnect
Global Services Daemon Control
starting gsdctl start
stopping gsdctl stop
status gsdctl status
Cluster Configuration (clscfg is used during installation)
create a new configuration clscfg -install
Note: the clscfg command is located in $ORA_CRS_HOME/bin
upgrade or downgrade and existing configuration
clscfg -upgradeclscfg -downgrade
add or delete a node from the configuration clscfg -addclscfg -delete
create a special single-node configuration for ASM
clscfg -local
brief listing of terminology used in the other nodes
clscfg -concepts
used for tracing clscfg -trace
help clscfg -h
Cluster Name Check
print cluster name
cemutlo -n
Note: in Oracle 9i the ulity was called "cemutls", the command is located in $ORA_CRS_HOME/bin
print the clusterware version cemutlo -w
Note: in Oracle 9i the ulity was called "cemutls"
Node Scripts
Add Node addnode.sh
Note: see adding and deleting nodes
Delete Node deletenode.sh
Note: see adding and deleting nodes
Oracle Cluster Registry (OCR)
As you already know the OCR is the registry that contains information
Node list Node membership mapping
Database instance, node and other mapping information
Characteristics of any third-party applications controlled by CRS
The file location is specified during the installation, the file pointer indicating the OCR device location is the ocr.loc, this can be in either of the following
linux - /etc/oracle solaris - /var/opt/oracle
The file contents look something like below, this was taken from my installation
orc.lococrconfig_loc=/u02/oradata/racdb/OCRFileocrmirrorconfig_loc=/u02/oradata/racdb/OCRFile_mirrorlocal_only=FALSE
OCR is import to the RAC environment and any problems must be immediately actioned, the command can be found in located in $ORA_CRS_HOME/bin
OCR Utilities
log file $ORA_HOME/log/<hostname>/client/ocrconfig_<pid>.log
checking
ocrcheck
Note: will return the OCR version, total space allocated, space used, free space, location of each device and the result of the integrity check
dump contents ocrdump
Note: by default it dumps the contents into a file named OCRDUMPFILE in the current directory
export/importocrconfig -export <file>
ocrconfig -restore <file>
backup/restore
# show backupsocrconfig -showbackup
# to change the location of the backup, you can even specify a ASM disk ocrconfig -backuploc <path|+asm>
# perform a backup, will use the location specified by the -backuploc location ocrconfig -manualbackup
# perform a restoreocrconfig -restore <file>
# delete a backuporcconfig -delete <file>
Note: there are many more option so see the ocrconfig man page
add/remove/replace
## add/relocate the ocrmirror file to the specified location ocrconfig -replace ocrmirror '/ocfs2/ocr2.dbf'
## relocate an existing OCR file ocrconfig -replace ocr '/ocfs1/ocr_new.dbf'
## remove the OCR or OCRMirror fileocrconfig -replace ocrocrconfig -replace ocrmirror
Voting Disk
The voting disk as I mentioned in the architecture is used to resolve membership issues in the event of a partitioned cluster, the voting disk protects data integrity.
querying crsctl query css votedisk
adding crsctl add css votedisk <file>
deleting crsctl delete css votedisk <file>
RAC Performance
I have already discussed basic Oracle tuning, in this section I will mainly dicuss Oracle RAC tuning. First lets review the best pratices of a Oracle design regarding the application and database
Optimize connection management, ensure that the middle tier and programs that connect to the database are efficent in connection management and do not log on or off repeatedly
Tune the SQL using the available tools such as ADDM and SQL Tuning Advisor
Ensure that applications use bind variables, cursor_sharing was introduced to solve this problem
Use packages and procedures (because they are compiled) in place of anonymous PL/SQL blocks and big SQL statements
Use locally managed tablespaces and automatic segment space management to help performance and simplify database administration
Use automatic undo management and temporary tablespace to simplify administration and increase performance
Ensure you use large caching when using sequences, unless you cannot afford to lose sequence during a crash
Avoid using DDL in production, it increases invalidations of the already parsed SQL statements and they need to be recompiled
Partion tables and indexes to reduce index leaf contention (buffer busy global cr problems)
Optimize contention on data blocks (hot spots) by avoiding small tables with too many rows in a block
Now we can review RAC specific best practices
Consider using application partitioning (see below) Consider restricting DML-intensive users to using one instance, thus reducing cache contention
Keep read-only tablespaces away from DML-intensive tablespaces, they only require minimum resources thus optimizing Cache Fusion performance
Avoid auditing in RAC, this causes more shared library cache locks
Use full tables scans sparingly, it causes the GCS to service lots of block requests, see table v$sysstat column "table scans (long tables)"
if the application uses lots of logins, increase the value of sys.audsess$ sequence
Partitioning Workload
Workload partitioning is a certian type of workload that is executed on an instance, that is partitioning allows users who access the same set of data to log on to the same instance. This limits the amount of data that is shared between instances thus saving resources used for messaging and Cache Fusion data block transfer.
You should consider the following when deciding to implement partitioning
If the CPU and private interconnects are of high performance then there is no need to to partition Partitioning does add complexity, thus if you can increase CPU and the interconnect performance the better
Only partition if performance is betting impacted
Test both partitioning and non-partitioning to what difference it makes, then decide if partitioning is worth it
RAC Wait Events
An event is an operation or particular function that the Oracle kernel performs on behalf of a user or a Oracle background process, events have specific names like database event. Whenever a session has to wait for something, the wait time is tracked and charged to the event that was associated with that wait. Events that are associated with all such waits are known as wait events. The are a number of wait classes
Commit Scheduler
Application
Configuration
User I/O
System I/O
Concurrency
Network
Administrative
Cluster
Idle
Other
There are over 800 different events spread across the above list, however you probably will only deal with about 50 or so that can improve performance.
When a session requests access to a data block it sends a request to the lock master for proper authorization, the request does not know if it will receive the block via Cache Fusion or a permission to read from the disk. Two placeholder events
global cache cr request (consistent read - cr) global cache curr request (current - curr)
keep track of the time a session spends in this state. There are number of types of wait events regarding access to a data block
Wait Event Contention
type Description
gc current block 2-way
write/write
an instance requests authorization for a block to be accessed in current mode to modify a block, the instance mastering the resource receives the request. The master has the current version of the block and sends the current copy of the block to the requestor via Cache Fusion and keeps a Past Image (.PI)
If you get this then do the following
Analyze the contention, segments in the "current blocks received" section of AWR Use application partitioning scheme
Make sure the system has enough CPU power
Make sure the interconnect is as fast as possible
Ensure that socket send and receive buffers are configured correctly
gc current block 3-way
write/write
an instance requests authorization for a block to be accessed in current mode to modify a block, the instance mastering the resource receives the request and forwards it to the current holder of the block, asking it to relinquish ownership. The holding instance sends a copy of the current version of the block to the requestor via Cache Fusion and transfers the exclusive lock to the requesting instance. It also keeps a past Image (PI).
Use the above actions to increase the performance
gc current block 2-way
write/read The difference with the one above is that this sends a copy of the block thus keeping the current copy.
gc current block 3-way
write/read The difference with the one above is that this sends a copy of the block thus keeping the current copy.
gc current block busy
write/write The requestor will eventually get the block via cache fusion but it is delayed due to one of the following
The block was being used by another session on another session
was delayed as the holding instance could not write the corresponding redo record immediately
If you get this then do the following
Ensure the log writer is tuned
gc current buffer busy
localThis is the same as above (gc current block busy), the difference is that another session on the same instance also has requested the block (hence local contention)
gc current block congested
none This is caused if heavy congestion on the GCS, thus CPU resources are stretched
Enqueue Tuning
Oracle RAC uses a queuing mechanism to ensure proper use of shared resources, it is called Global Enqueue Services (GES). Enqueue wait is the time spent by a session waiting for a shared resource, here are some examples of enqueues:
updating the control file (CF enqueue) updating an individual row (TX enqueue)
exclusive lock on a table (TM enqueue)
Enqueues can be managed by the instance itself others are used globally, GES is responsible for coordinating the global resources. The formula used to calculate the number of enqueue resources is as below
GES Resources = DB_FILES + DML_LOCKS + ENQUEUE_RESOURCES + PROCESS + TRANSACTION x (1 + (N - 1)/N)
N = number of RAC instances
displaying enqueues stats
SQL> column current_utilization heading currentSQL> column max_utilization heading max_usageSQL> column initial_allocation heading initialSQL> column resource_limit format a23;
SQL> select * from v$resource_limit;
AWR and RAC
I have already discussed AWR in a single instance environment, so for a quick refresh take a look and come back here to see how you can use it in a RAC environment.
From a RAC point of view there are a number of RAC-specific sections that you need to look at in the AWR, in the report section is a AWR of my home RAC environment, you can view the whole report here.
RAC AWR Section Report Description
Number of Instances instances lists the number of instances from the beginning and end of the AWR report
Instance global cache load profile
global cache information about the interinstance cache fusion data block and messaging traffic, because my AWR reportlightweight here is a more heavy used RAC example
Global Cache Load Profile~~~~~~~~~~~~~~~~~~~~~~~~~ Per Second Per Transaction --------------- ---------------Global Cache blocks received: 315.37 12.82Global Cache blocks served: 240.30 9.67GCS/GES messages received: 525.16 20.81GCS/GES messages sent: 765.32 30.91
The first two statistics indicate the number of blocks transferred to or from this instance, thus if you are using a 8K block size
Sent: 240 x 8,192 = 1966080 bytes/sec = 2.0 MB/sec Received: 315 x 8,192 = 2580480 bytes/sec = 2.6 MB/sec
to determine the amount of network traffic generated due to messaging you first need to find the average message size (this was 193 on my system)
select sum(kjxmsize * (kjxmrcv + kjxmsnt + kjxmqsnt)) / sum((kjxmrcv + kjxmsnt + kjxmqsnt)) "avg Message size" from x$kjxm where kjxmrcv > 0 or kjxmsnt > 0 or kjxmqsnt > 0;
then calculate the amount of messaging traffic on this network
193 (765 + 525) = 387000 = 0.4 MB
to calculate the total network traffic generated by cache fusion
= 2.0 + 2.6 + 0.4 = 5 MBytes/sec = 5 x 8 = 40 Mbits/sec
The DBWR Fusion writes statistic indicates the number of times the local DBWR was forced to write a block to disk due to remote instances, this number should be low.
Glocal cache efficiency percentage
global cache efficiency
this section shows how the instance is getting all the data blocks it needs. The best order is the following
Local cache Remote cache
Disk
The first two give the cache hit ratio for the instance, you are looking for a value less than 10%, if you are getting higher values then you may consider application partitioning.
GCS and GES - workload characteristics
GCS and GES workload
this section contains timing statistics for global enqueue and global cache. As a general rule you are looking for
All timings related to CR (Consistent Read) processing block should be less than 10 msec
All timings related to CURRENT block processing should be less than 20 msec
Messaging statistics messaging The first section relates to sending a message and should be less than 1 second.
The second section details the breakup of direct and indirect messages, direct messages are sent by a instance foreground or the user processes to remote instances, indirect are messages that are not urgent and are pooled and sent.
Service statistics Service stats shows the resources used by all the service instance supports
Service wait class statistics
Service wait class summarizes waits in different categories for each service
Top 5 CR and current block segements
Top 5 CR and current blocks
conatns the names of the top 5 contentious segments (table or index). If a table or index has a very high percentage of CR and Current block transfers you need to investigate. This is pretty much like a normal single instance.
Cluster Interconnect
As I stated above the interconnect it a critical part of the RAC, you must make sure that this is on the best hardware you can buy. You can confirm that the interconnect is being used in Oracle 9i and 10g by using the command oradebug to dump information out to a trace file, in Oracle 10g R2 the cluster interconnect is also contained in the alert.log file, you can view my information from here.
interconnect
SQL> oradebug setmypidSQL> oradebug ipc
Note: look in the user_dump_dest directory, the trace will be there
Global Resource Directory (GRD)
The RAC environment includes many resources such as multiple versions of data block buffers in buffer caches in different modes, Oracle uses locking and queuing mechanisms to coordinate lock resources, data and interinstance data requests. Resources such as data blocks and locks must be synchronized between nodes as nodes within a cluster acquire and release ownership of them. The synchronization provided by the Global Resource Directory (GRD) maintains a cluster wide concurrency of the resources and in turn ensures the integrity of the shared data. Synchronization is also required for buffer cache management as it is divided into multiple caches, and each instance is responsible for managing its own local version of the buffer cache. Copies of data are exchanged between nodes, this sometimes is referred to as the global cache but in reality each nodes buffer cache is separate and copies of blocks are exchanged through traditional distributed locking mechanism.
Global Cache Services (GCS) maintain the cache coherency across buffer cache resources and Global Enqueue Services (GES) controls the resource management across the clusters non-buffer cache resources.
Cache Coherency
Cache coherency identifies the most up-to-date copy of a resource, also called the master copy, it uses a mechanism by which multiple copies of an object are keep consistent between Oracle instances. Parallel Cache Management (PCM) ensures that the master copy of a data block is stored in one buffer cache and consistent copies of the data block are stored in other buffer caches, the process LCKx is responsible for this task.
The lock and resource structures for instance locks reside in the GRD (also called the DLM), its a dedicated area within the shared pool. Details about the data blocks resources and cached versions are maintained by GCS. Additional details such as the location of the most current version, state of the buffer, role of the data block (local or global) and ownership are maintained by GES. Global cache together with GES form the GRD. Each instance maintains a part of the GRD in its SGA. The GCS and GES nominate one instance, this will become the resource master, to manage all information about a particular resource. Each instance knows which instance master is with which resource.
Resources and Enqueues
A resource is an identifiable entity, it has a name or reference. The referenced entity is usually a memory region, a disk file, a data block or an abstract entity. A resource can be owned or locked in various states (exclusive or shared), all resources are lockable. A global resource is visible throughout the cluster, thus a local resource can only be used by the instance at it is local too. Each resource can have a list of locks called the grant queue, that are currently granted to users. A convert queue is a queue of locks that are waiting to be converted to particular mode, this is the process of changing a lock from one mode to another, even a NULL is a lock. A resource has a lock value block (LVB). The Global Resource Manager (GRM) keeps the lock information valid and correct across the cluster.
Locks are placed on a resource grant or a convert queue, if the lock changes it moves between the queues. A lock leaves the convert queue under the following conditions
The process requests the lock termination (it remove the lock) The process cancels the conversion, the lock is moved back to the grant queue in the previous mode
The requested mode is compatible with the most restrictive lock in the grant queue and with all the previous modes of the convert queue, and the lock is at the head of the convert queue
Convert requests are processed on a FIFO basis, the grant queue and convert queue are associated with each and every resource that is managed by the GES.
Enqueues are basically locks that support queuing mechanisms and that can be acquired in different modes. An enqueue can be held in exclusive mode by one process and others can hold a non-exclusive mode depending on the type. Enqueues are the same in RAC as they are in a single instance.
Global Enqueue Services (GES)
GES coordinates the requests of all global enqueues, it also deals with deadlocks and timeouts. There are two types of local locks, latches and enqueues, latches do not affect the cluster only the local instance, enqueues can affect both the cluster and the instance.
Enqueues are shared structures that serialize access to database resources, they support multiple modes and are held longer than latches, they protect persistent objects such as tables or library cache objects. Enqueues can use any of the following modes
Mode Summary Description
NULL NULL no access rights, a lock is held at this level to indicate that a process is interested in a resource
SS SubSharedthe resource can be read in an unprotected fashion other processes can read and write to the resource, the lock is also known as a row share lock
SXShared
Exclusive the resource can be read and written to in an unprotected fashion, this is also known as a RX (row exclusive) lock
S Shared a process cannot write to the resource but multiple processes can read it. This is the traditional share lock.
SSXSubShared Exclusive
Only one process can hold a lock at this level, this makes sure that only processes can modify it at a time. Other processes can perform unprotected reads. This is also know as a SRX (shared row exclusive) table lock.
X Exclusivegrants the holding process exclusive access to the resource, other processes cannot read or write to the resource. This is also the traditional exclusive lock.
Global Locks
Each node has information for a set of resources, Oracle uses a hashing algorithm to determine which nodes hold the directory tree information for the resource. Global locks are mainly of two types
Locks used by the GCS for buffer cache management, these are called PCM locks Global locks (global enqueue) that Oracle synchronizes within a cluster to coordinate non-PCM resources, they protect the
enqueue structures
An instance owns a global lock that protects a resource (i.e. data block or data dictionary entry) when the resource enters the instance's SGA.
GES locks control access to data files (not the data blocks) and control files and also serialize interinstance communication. They also control library caches and the dictionary cache. Examples of this are DDL, DML enqueue table locks, transaction enqueues and DDL locks or dictionary locks. The SCN and mount lock are global locks.
Transaction and row locks are the same as in a single instance database, the only difference is that the enqueues are global enqueues, take a look in locking for an in depth view on how Oracle locking works.
Messaging
The difference between RAC and a single instance messaging is that RAC uses the high speed interconnect and a single instance uses shared memory and semaphores, interrupts are used when one or more process want to use the processor in a multiple CPU architecture. GES uses messaging for interinstance communication, this is done by messages and asynchronous traps (ASTs). Both LMON and LMD use messages to communicate to other instances, the GRD is updated when locks are required. The messaging traffic can be viewed using the view V$GES_MISC.
A three-way lock message involves up to a maximum of three instances, Master instance (M), Holding instance (H) and the Requesting instance (R), the sequence is detailed below where requesting instance R is interested in block B1 from holding instance H. The resource is mastered in master instance M
1. Instance R gets the ownership information about a resource from the GRD, instance R then sends the message to the master instance M requesting access to the resource. This message is sent by a direct send as it is critical
2. Instance M receives the message and forwards it to the holding instance H. This is also sent directly, this is known as a blocking asynchronous trap (BAST).
3. Instance H sends the resource to instance R, using the interconnect, the resource is copied in instance R memory
4. Once the lock handle is obtained on the resource instance R sends an acknowledgment to instance M. This message is queued as it is not critical, this is called acquisition asynchronous trap (AAST).
Because GES heavily rely's on messaging the interconnect must be of high quality (high performance , low latency), also the messages are kept small (128 bytes) to increase performance. The Traffic Controller (TRFC) is used to control the DLM traffic between the instances in the cluster, it uses buffering to accommodate large volumes of traffic. The TRFC keeps track of everything by using tickets (sequence numbers), there is a predefined pool of tickets this is dependent on the network send buffer size. A ticket is obtained before sending any messages, once sent the ticket is returned to the pool, LMS or LMD perform this. If there are no tickets then the message has to wait until a ticket is available. You can control the number of tickets and view them
system parameter _lm_tickets_lm_ticket_active_sendback (used for aggressive messaging)
ticket usageselect local_nid local, remote_nid remote, tckt_avail avail, tckt_limit limit, snd_q_len send_queue, tckt_wait waiting from v$ges_traffic_controller;
dump ticket information
SQL> oradebug setmypidSQL> oradebug unlimitSQL> oradebug lkdebug -t
Note: the output can be viewed here
Global Cache Services (GCS)
GCS locks only protect data blocks in the global cache (also know as PCM locks), it can be acquired in share or exclusive mode. Each lock element can have the lock role set to either local (same as single instance) or global. When in global role three lock modes are possible, shared, exclusive and null. In global role mode you can read or write to the data block only as directed by the master instance of that resource. The lock and state information is held in the SGA and is maintained by GCS, these are called lock elements. It also holds a chain of cache buffer chains that are covered by the corresponding lock elements. These can be view via v$lock_element, the parameter _db_block_hash_buckets controls the number of hash buffer chain buckets.
GCS locks uses the following modes as stated above
Exclusive (X) used during update or any DML operation, if another instance requires the block that has a exclusive lock it asks GES to request that he second instance disown the global lock
Shared (S) used for select operations, reading of data does not require a instance to disown a global lock.
Null (N) allows instances to keep a lock without any permission on the block(s). This mode is used so that locks need not be created and destroyed all the time, it just converts from one lock to another.
Lock roles are used by Cache Fusion, it can be either local or global, the resource is local if the block is dirty only in the local cache, it is global if the block is dirty in a remote cache or in several remote caches. A Past Image (PI) is kept by the instance when a block is shipped to another instance, the role is then changed to a global role, thus the PI represents the state of a dirty buffer. A node must keep a PI until it receives notification from the master that a write to disk has completed covering that version, the node will then log a block written record (BWR). I have already discussed PI and BWR in my backup section.
When a new current block arrives, the previous PI remains untouched in case another node requires it. If there are a number of PI's that exist, they may or may not merge into a single PI, the master will determine this based on if the older PI's are required, a indeterminate number of PI's can exist.
In the local role only S and X modes are permitted, when requested by the master instance the holding instance serves a copy of the block to others. If the block is globally clean this instance lock role remains local. If the block is modified (dirty), a PI is retained and the lock becomes global. In the global lock role lock modes can be N, S and X, the block is global and it may even by dirty in any of
the instances and the disk version may be obsolete. Interested parties can only modify the block using X mode, an instance cannot read from the disk as it may not be current, the holding instance can send copies to other instances when instructed by the master.
I have a complete detailed walkthough in my cache_fusion section, which will help you better to understand.
A lock element holds lock state information (converting, granting, etc). LEs are managed by the lock process to determine the mode of the locks, they also old a chain of cache buffers that are covered by the LE and allow the Oracle database to keep track of cache buffers that must be written to disk in a case a LE (mode) needs to be downgraded (X > N).
LEs protect all the data blocks in the buffer cache, the list below describes the classes of the data block which are managed by the LEs using GCS locks (x$bh.class).
0 FREE
1 EXLCUR
2 SHRCUR
3 CR
4 READING
5 MRECOVERY
6 IRCOVERY
7 WRITING
8 PI
So putting this altogether you get the following, GCS manages PCM locks in the GRD, PCM locks manage the data blocks in the global cache. Data blocks are can be kept in any of the instances buffer cache (which is global), if not found then it can be read from disk by the requesting instance. The GCS monitors and maintains the list and mode of the blocks in all the instances. Each instance will master a number of resources, but a resource can only be mastered by one instance. GCS ensures cache coherency by requiring that instances acquire a lock before modifying or reading a database block. GCS locks are not row-level locks, row-level locks are used in conjunction with PCM locks. GCS lock ensures that they block is accessed by one instances then row-level locks manage the blocks at the row-level. If a block is modified all Past Images (PI) are no longer current and new copies are required to obtained.
Consistent read processing means that readers never block writers, as the same in a single instance. One parameter that can help is _db_block_max_cr_dba which limits the number of CR copies per DBA on the buffer cache. If too many CR requests arrive for a particular buffer, the holder can disown the lock on the buffer and write the buffer to the disk, thus the requestor can then read it from disk, especially if the requested block has a older SCN and needs to reconstruct it (known as CR fabrication). This is technically known as fairness downconvert, and the parameter _fairness_threshold can used to configure it.
The lightwork rule is involved when CR construction involves too much work and no current block or PI block is available in the cache for block cleanouts. The below can be used to view the number of times a downconvert occurs
downconvertselect cr_requests, light_works, data_requests, fairness_down_converts from v$cr_block_server;
Note: lower the _fairness_threshold if the ratio goes above 40%, set to 0 if the instance is a query only instance.
The GRD is a central repository for locks and resources, it is distributed across all nodes (not a single node), but only one instance masters a resource. The process of maintaining information about resources is called lock mastering or resource mastering. I spoke about lock remastering in my backup section.
Resource affinity allows the resource mastering of the frequently used resources on its local node, it uses dynamic resource mastering to move the location of the resource masters. Normally resource mastering only happens when a instance joins or leaves the RAC environment, as of Oracle 10g R2 mastering occurs at the object level which helps fine-grained object remastering. There are a number of parameters that can be used to dynamically remaster an object
_gc_affinity_time specifies interval minutes for remastering
_gc_affinity_limit defines the number of times a instance access the resource before remastering, setting to 0 disable remastering
_gc_affinity_minimum defines the minimum number of times a instance access the resource before remastering
_lm_file_affinity disables dynamic remastering for the objects belonging to those files
_lm_dynamic_remastering enable or disable remastering
You should consult Oracle before changing any of the above parameters.
Cache Fusion
I mentioned above Cache Fusion in my GRD section, here I go into great detail on how it works, I will also provide a number of walk through examples on my RAC system.
Cache Fusion uses the most efficient communications as possible to limit the amount of traffic used on the interconnect, now you don't need this level of detail to administer a RAC environment but it sure helps to understand how RAC works when trying to diagnose problems. RAC appears to have one large buffer but this is not the case, in reality the buffer caches of each node remain separate, data blocks are shared through distributed locking and messagingoperations. RAC copies data blocks across the interconnect to other instances as it is more efficient than reading the disk, yes memory and networking together are faster than disk I/O.
Ping
The transfer of a data block from instances buffer cache to another instances buffer cache is know as a ping. As mentioned already when an instance requires a data block it sends the request to the lock master to obtain a lock in the desired mode, this process is known as blocking asynchronous trap (BAST). When an instance receives a BAST it downgrades the lock ASAP, however it might have to write the corresponding block to disk, this operation is known as disk ping or hard ping. Disk pings have been reduce in the later versions of RAC, thus relaying on block transfers more, however there will always be a small amount of disk pinging. In the newer versions of RAC when a BAST is received sending the block or downgrading the lock may be deferred by tens of milliseconds,
this extra time allows the holding instance to complete an active transaction and mark the block header appropriately, this will eliminate any need for the receiving instance to check the status of the transaction immediately after receiving/reading a block. Checking the status of a transaction is an expensive operation that may require access (and pinging) to the related undo segment header and undo data blocks as well. The parameter _gc_defer_time can be used to define the duration by which an instance deferred downgrading a lock.
Past Image Blocks (PI)
In the GRD section I mentioned Past Images (PIs), basically they are copies of data blocks in the local buffer cache of an instance. When an instance sends a block it has recently modified to another instance, it preserves a copy of that block, marking as a PI. The PI is kept until that block is written to disk by the current owner of the block. When the block is written to disk and is known to have a global role, indicating the presents of PIs in other instances buffer caches, GCS informs the instance holding the PIs to discard the PIs. When a checkpoint is required it informs GCS of the write requirement, GCS is responsible for finding the most current block image and informing the instance holding that image to perform a block write. GCS then informs all holders of the global resource that they can release the buffers holding the PI copies of the block, allowing the global resource to be released. You can view the past image blocks present in the fixed table X$BH
PIs
select state, count(state) from X$BH group by state;
Note: the state column with 8 is the past images.
Cache Fusion I
Cache Fusion I is also know as consistent read server and was introduced in Oracle 8.1.5, it keeps a list of recent transactions that have changed a block.the original data contained in the block is preserved in the undo segment, which can be used to provide consistent read versions of the block.
In a single instance the following happens when reading a block
When a reader reads a recently modified block, it might find an active transaction in the block The reader will need to read the undo segment header to decide whether the transaction has been committed or not
If the transaction is not committed, the process creates a consistent read (CR) version of the block in the buffer cache using the data in the block and the data stored in the undo segment
If the undo segment shows the transaction is committed, the process has to revisit the block and clean out the block (delay block cleanout) and generate the redo for the changes.
In an RAC environment if the process of reading the block is on an instance other than the one that modified the block, the reader will have to read the following blocks from the disk
data block to get the data and/or transaction ID and Undo Byte Address (UBA) undo segment header block to find the last undo block used for the entire transaction
undo data block to get the actual record to construct a CR image
Before these blocks can be read the instance modifying the block will have to write those's blocks to disk, resulting in 6 I/O operations. In RAC the instance can construct a CR copy by hopefully using the above blocks that are still in memory and then sending the CR over the interconnect thus reducing 6 I/O operations.
As from Oracle 8 introduced a new background process called the Block Server Process makes the CR fabrication at the holders cache and ships the CR version of the block across the interconnect, the sequence is detailed in the table below
1. An instance sends a message to the lock manager requesting a shared lock on the block
2. Following are the possibilities in the global cache
o If there is no current user for the block, the lock manager grants the shared lock to the requesting instance
o if the other instance has an exclusive lock on the block, the lock manager asks the owning instance to build a CR copy and ship it to the requesting instance.
3. Based on the result, either of the following can happen
o if the lock is granted, the requesting instance reads the block from disk
o The owning instance creates a CR version of the buffer in its own buffer cache and ships it to the requesting instance over the interconnect
4. The owning instance also informs the lock manager and requesting instance that it has shipped the block
5. The requesting instance has the locked granted, the lock manager updates the IDLM with the new holders of that resource
While making a CR copy, the holding instance may refuse to do so if
it does not find any of the blocks needed in its buffer cache, it will not perform a disk read to make a CR copy for another instance
It is repeatedly asked to send a CR copy of the same block, after sending the CR copies four times it will voluntarily relinquish the lock, write the block to the disk and let other instances get the block from the disk. The number of copies it will serve before doing so is governed by the parameter _fairness_threshold
Cache Fusion II
Read/Write contention was addressed in cache fusion I, cache fusion II addresses the write/write contention
1. An instance sends a message to the lock manager requesting an exclusive lock on the block
2. Following are the possibilities in the global cache
o If there is no current user for the block, the lock manager grants the exclusive lock to the requesting instance
o if the other instance has an exclusive lock on the block, the lock manager asks the owning instance to release the lock
3. Based on the result, either of the following can happen
o if the lock is granted, the requesting instance reads the block from disk
o The owning instance sends the current block to the requesting instance via the interconnect, to guarantee recovery in the event of instance death, the owning instance writes all the redo records generated for the block to the online redolog file. It will keep a past image of the block and inform the master instance that it has sent the current block to the requesting instance
4. The lock manager updates the resource directory (GRD) with the current holder of the block
Cache Fusion in Operation
A quick recap of GCS, a GCS resource can be local or global, if it is local it can be acted upon without consulting other instances, if it is global it cannot be acted upon without consulting or informing remote instances. GCS is used as a messaging agent to coordinate manipulation of a global resource. By default all resources are in NULL mode (remember null mode is used to convert from one type to another (share or exclusive)).
The table below denotes the different states of a resource
Mode/Role Local Global
Null (N) NL NG
Shared (S) SL SG
Exclusive (X) XL XG
States
SLit can serve a copy of the block to other instances and it can read the block from disk, since the block is not modified there is no need to write to disk
XL
it has sole ownership and interest in that resource, it has exclusive right to modify the block, all changes to the blocks are in the local buffer cache and it can write the block to the disk. If another instance wants the block it can to come via the GCS
NLused to protect consistent read block, if an instance wants it in X mode, the current instance will send the block to the requesting instance and downgrades its role to NL
SGa block is present in one or more instances, an instance can read the read from disk and serve it to other instances
XG
a block can have one or more PIs, the instance with the XG role has the latest copy of the block and is the most likely candidate to write the block to the disk. GCS can ask the instance to write the block and serve it to other instances
NGafter discarding PIs when instructed to by GCS, the block is kept in the buffer cache with NG role, this serves only as the CR copy of the block.
Below are a number of common scenarios to help understand the following
reading from disk reading from cache
getting the block from cache for update
performing an update on a block
performing an update on the same block
reading a block that was globally dirty
performing a rollback on a previously updated block
reading the block after commit
We will assume the following
Four RAC environment (Instances A, B, C and D) Instance D is the master of the lock resource for the data block BL
We will only use one block and it will reside at SCN 987654
We will use a three-letter code for the lock states
o first letter will indicate the lock mode - N = Null, S = Shared and X = Exclusive
o second latter will indicate lock role - G = Global, L = Local
o The third letter will indicate the PIs - 0 = no PIs, 1 = a PI of the bloc
for example a code of SL0 means a global shared lock with no past images (PIs)
Reading a block from disk
instance C want to read the block it will request a lock in share mode from the master instance
1. Instance C requests the block by sending a shared lock request to master D
2. The block has never been read into the buffer cache of any instance and it is not locked. Master D grants the lock to instance C. The lock granted is SL0 (see above to work out three-letter code)
3. Instance C reads the block from the shared disk into its buffer cache
4. Instance C has the block in shard mode, the lock manager updates the resource directory.
Reading a block from the cache
Carrying on from the above example, Instance B wants to read the same block that is cached in instance C buffer.
1. Instance B sends a shared lock request to master instance D2. The lock master knows that the block may be available at instance
C and sends a ping message to instance C
3. Instance C sends the block to instance B via the interconnect, along with the block instance C indicates that instance B should take the current lock mode and role from instance C, instance C keeps a copy of the block
4. Instance B sends a message to instance D that it has assumed the SL lock for the block. This message is not critical for the lock manager, thus the message is sent asynchronously
Getting a (Cached) clean block for update
Carrying on from the above example, instance A wants to modify the same block that is already cached in instance B and C (block 987654)
1. Instance A sends an exclusive lock request to master D2. The lock master knows that the block may be available at instance
B in SCUR mode and at instance C in CR mode. it also sends a ping message to the shared lock holders. The most recent access was at instance B and instance D sends a BAST message to instance B
3. Instance B sends the block to instance A via the interconnect and closes it shared lock. The block may still be in its buffer to be as CR, but all locks are released
4. Instance A now has the exclusive lock on the block and sends an assume message to instance D, the lock is in XL0
5. Instance A modifies the block in its buffer cache, the changes are not committed and thus the block has not been written to disk, thus the SCN remains at 987654
Getting a (Cached) modified block for update and commit
Carrying on from the above example, instance C now wants to modify the block, if it tries to modify the same row it will have to wait until instance A either commits or rolls back. However in this case instance C wants to modify a different row in the same block.
1. Instance C sends an exclusive lock request to master D2. The lock master knows that instance A holds an exclusive lock on
the block and hence sends a ping message to instance A
3. Instance A sends the dirty buffer to instance C via the interconnect, it downgrades the lock from XCR to NULL, it keeps a PI version of the block and disowns any lock on that buffer. Before shipping
the block, Instance A has to create a PI image and flush any pending redo for the block change, the block mode on instance A is now NG1
4. Instance C sends a message to instance D indicating it has the block in exclusive mode. The block role G indicates that the block is in global mode and if it needs to write the block to disk it must coordinate it with other instances that have past images (PIs) of that block. Instance C modifies the block and issues a commit, the SCN is now 987660.
Commit the previously modified block and select the data
Carrying on from the above example, instance A now issues a commit to release the row level locks held by the transaction and flush the redo information to the redologs
1. Instance A wants to commit the changes, commit operations do not require any synchronous modifications to the block
2. The lock status remains the same as the previous state and change vectors for the commits are written to the redologs.
Write the dirty buffers to disk due to a checkpoint
Carrying on from the above example, instance B writes the dirty blocks from the buffer cache due to a checkpoint (this is were it gets interesting and very clever)
1. Instance B sends a write request to master D with the necessary SCN
2. The master knows that the most recent copy of the block may be available at instance C and hence sends a message to instance C asking to write
3. Instance C initiates a disk write and writes a BWR into the redolog file
4. Instance C get the write notification that the write is complete
5. Instance C notifies the master that the write is completed
6. On receipt of the notification, instance D tells all PI holders to discard their PIs, and the lock at instance C writes the modified block to the disk
7. All instances that have previously modified this block will also have to write a BWR. The write request by instance C has now been satisfied and instance C can now proceed with its checkpoint as usual
Master instance crashes
Carrying on from the above example
1. the master instance D crashes
2. The Global Resource Directory is frozen momentarily and the resources held by master instance D will be equally distributed in the surviving nodes, also know as remastering (see remastering for more details).
Select the rows from Instance A
Carrying on from the above example, now instance A queries the rows from that table to get the most recent data
1. Instance A sends a shared lock to now the new master instance C2. Master C knows the most recent copy of the block may be in
instance C and asks the holder to ship the CR block to instance A
3. Instance C ships the CR block to instance A via the interconnect
The above sequence of events can be seen in the table below
ExampleOperation on Node Buffer Status
A B C D A B C D
1 read block from SCUR
disk
2read the block from
cache CR SCUR
3 update the block XCUR CR CR
4update the same
block PI CR XCUR
5commit the
changes PI CR XCUR
6 trigger checkpoint CR XCUR
7instance
crash
8 select the rows CR XCUR
RAC Troubleshooting
This is the one section what will be updated frequently as my experience with RAC grows, as RAC has been around for a while most problems can be resolve with a simple google lookup, but a basic understanding on where to look for the problem is required. In this section I will point you where to look for problems, every instance in the cluster has its own alert logs, which is where you would start to look. Alert logs contain startup and shutdown information, nodes joining and leaving the cluster, etc.
Here is my complete alert log file of my two node RAC starting up.
The cluster itself has a number of log files that can be examined to gain any insight of occurring problems, the table below describes the information that you may need of the CRS components
$ORA_CRS_HOME/crs/log contains trace files for the CRS resources
$ORA_CRS_HOME/crs/init contains trace files for the CRS daemon during startup, a good place to start
$ORA_CRS_HOME/css/logcontains cluster reconfigurations, missed check-ins, connects and disconnects from the client CSS listener. Look here to obtain when reboots occur
$ORA_CRS_HOME/css/init contains core dumps from the cluster synchronization service daemon (OCSd)
$ORA_CRS_HOME/evm/log log files for the event volume manager and eventlogger daemon
$ORA_CRS_HOME/evm/init pid and lock files for EVM
$ORA_CRS_HOME/srvm/log log files for Oracle Cluster Registry (OCR)
$ORA_CRS_HOME/log log files for Oracle clusterware which contains diagnostic messages at the Oracle cluster level
As in a normal Oracle single instance environment, a RAC environment contains the standard RDBMS log files, these files are located by the parameter background_dest_dump. The most important of these are
$ORACLE_BASE/admin/udump contains any trace file generated by a user process
$ORACLE_BASE/admin/cdump contains core files that are generated due to a core dump in a user process
Now lets look at a two node startup and the sequence of events
First you must check that the RAC environment is using the connect interconnect, this can be done by either of the following
logfile## The location of my alert log, yours may be different /u01/app/oracle/admin/racdb/bdump/alert_racdb1.log
ifcfg command oifcfg getif
table check select inst_id, pub_ksxpia, picked_ksxpia, ip_ksxpia from x$ksxpia;
oradebug
SQL> oradebug setmypidSQL> oradebug ipc
Note: check the trace file which can be located by the parameter user_dump_dest
system parameter cluster_interconnects
Note: used to specify which address to use
When the instance starts up the Lock Monitor's (LMON) job is to register with the Node Monitor (NM) (see below table). Remember when a node joins or leaves the cluster the GRD undergoes a reconfiguration event, as seen in the logfile it is a seven step process (see below for more details on the seven step process).
The LMON trace file also has details about reconfigurations it also details the reason for the event
reconfiguation reason description
1 means that the NM initiated the reconfiguration event, typical when a node joins or leaves a cluster
2
means that an instance has died
How does the RAC detect an instance death, every instance updates the control file with a heartbeat through its checkpoint (CKPT), if the heartbeat information is missing for x amount of time, the instance is considered to be dead and the Instance Membership Recovery (IMR) process initiates reconfiguration.
3means communication failure of a node/s. Messages are sent across the interconnect if a message is not received in an amount of time then a communication failure is assumed by default UDP is used and can be unreliable so keep an eye on the logs if too many reconfigurations happen for reason 3.
Example of a reconfiguration, taken from the alert log.
Sat Mar 20 11:35:53 2010Reconfiguration started (old inc 2, new inc 4)List of nodes: 0 1 Global Resource Directory frozen * allocate domain 0, invalid = TRUE Communication channels reestablished Master broadcasted resource hash value bitmaps Non-local Process blocks cleaned outSat Mar 20 11:35:53 2010 LMS 0: 0 GCS shadows cancelled, 0 closed Set master node info Submitted all remote-enqueue requests Dwn-cvts replayed, VALBLKs dubious All grantable enqueues granted Post SMON to start 1st pass IR
Sat Mar 20 11:35:53 2010 LMS 0: 0 GCS shadows traversed, 3291 replayedSat Mar 20 11:35:53 2010 Submitted all GCS remote-cache requests Post SMON to start 1st pass IR Fix write in gcs resourcesReconfiguration complete
Note: when a reconfiguration happens the GRD is frozen until the reconfiguration is completed
Confirm that the database has been started in cluster mode, the log file will state the following
cluster mode Sat Mar 20 11:36:02 2010Database mounted in Shared Mode (CLUSTER_DATABASE=TRUE)Completed: ALTER DATABASE MOUNT
Staring with 10g the SCN is broadcast across all nodes, the system will have to wait until all nodes have seen the commit SCN. You can change the board cast method using the system parameter _lgwr_async_broadcasts.
Lamport Algorithm
The lamport algorithm generates SCNs in parallel and they are assigned to transaction on a first come first served basis, this is different than a single instance environment, a broadcast method is used after a commit operation, this method is more CPU intensive as it has to broadcast the SCN for every commit, but he other nodes can see the committed SCN immediately.
The initialization parameter max_commit_propagation_delay limits the maximum delay allow for SCN propagation, by default it is 7 seconds. When set to less than 100 the broadcast on commit algorithm is used.
Disable/Enable Oracle RAC
There are times when you may wish to disable RAC, this feature can only be used in a Unix environment (no windows option).
Disable Oracle RAC (Unix only)
1. Log in as Oracle in all nodes
2. shutdown all instances using either normal or immediate option
3. change to the working directory $ORACLE_HOME/lib
4. run the below make command to relink the Oracle binaries without the RAC option (should take a few minutes)
make -f ins_rdbms.mk rac_off
5. Now relink the Oracle binaries
make -f ins_rdbms.mk ioracle
Enable Oracle RAC (Unix only)
1. Log in as Oracle in all nodes
2. shutdown all instances using either normal or immediate option
3. change to the working directory $ORACLE_HOME/lib
4. run the below make command to relink the Oracle binaries without the RAC option (should take a few minutes)
make -f ins_rdbms.mk rac_on
5. Now relink the Oracle binaries
make -f ins_rdbms.mk ioracle
Performance Issues
Oracle can suffer a number of different performance problems and can be categorized by the following
Hung Database Hung Session(s)
Overall instance/database performance
Query Performance
A hung database is basically an internal deadlock between to processes, usually Oracle will detect the deadlock and rollback one of the processes, however if the situation occurs with the internal kernel-level resources (latches or pins), it is unable to automatically detect and resolve the deadlock, thus hanging the database. When this event occurs you must obtain dumps from each of the instances (3 dumps per instance in regular times), the trace files will be very large.
capture information
## Using alter session SQL> alter session set max_dump_file_size = unlimited;SQL> alter session set events 'immediate trace name systemstate level 10';
# using oradebugSQL> select * from dual;SQL> oradebug setmypidSQL> unlimitSQL> oradebug dump systemstate 10
# using oradebug from another instanceSQL> select * from dual;SQL> oradebug setmypidSQL> unlimitSQL> oradebug -g all dump systemstate 10
Note: the select statement above is to avoid problems on pre 8 Oracle
SQLPlus - problems connecting
## If you get problems connecting with SQLPLUS use the command below$ sqlplus -prelimEnter user-name: / as sysdba
A severe performance problem can be mistaken for a hang, this usually happen because of contention problems, a systemstate dump is normally used to analyze this problem, however a systemstate dump taken a long time to complete, it also has a number of limitations
Reads the SGA in a dirty manner, so it may be inconsistent Usually dumps a lot of information
does not identify interesting processes on which to perform additional dumps
can be a very expensive operation if you have a large SGA.
To overcome these limitations a new utility command was released with 8i called hanganalyze which provides clusterwide information in a RAC environment on a single shot.
sql method alter session set events 'immediate trace hanganalyze level <level>';
oradebug
SQL> oradebug hanganalyze <level>
## Another way using oradebugSQL> setmypidSQL> setinst allSQL> oradebug -g def hanganalyze <level>
Note: you will be told where the output will be dumped to
hanganalyze levels
1-2 only hanganalyze output, no process dump at all, click here for an example level 1 dump
3 Level 2 + Dump only processes thought to be in a hang (IN_HANG state)
4 Level 3 + Dump leaf nodes (blockers) in wait chains (LEAF, LEAF_NW, IGN_DMP state)
5 Level 4 + Dump all processes involved in wait chains (NLEAF state)
10 Dump all processes (IGN state)
The hanganalyze command uses internal kernel calls to determine whether a session is waiting for a resource and reports the relationship between blockers and waiters, systemdump is better but if you over whelmed try hanganalyze first.
Debugging Node Eviction
A node is evicted from the cluster after it kills itself because it is not able to service the application, this generally happens when you have communication problems. For eviction node problems look for ora-29740 errors in the alert log file and LMON trace files.
To understand eviction problems you need to now the basics of node membership and instance membership recovery (IMR) works. When a communication failure happens the heartbeat information in the control cannot happen, thus data corruption can happen. IMR will remove any nodes from the cluster that it deems as a problem, IMR will ensure that the larger part of the cluster will survive and kills any remaining nodes. IMR is part of the service offered by Cluster Group Services (CGS). LMON handles many of the CGS functionalities, this works at the cluster level and can work with 3rd party software (Sun Cluster, Veritas Cluster). The Node Monitor (NM) provides information about nodes and their health by registering and communicating with the Cluster Manager (CM). Node membership is represented as a bitmap in the GRD. LMON will let other nodes know of any changes in membership, for example if a node joins or leaves the cluster, the bitmap is rebuilt and communicated to all nodes.
Node registering (alert log)
lmon registered with NM - instance id 1 (internal mem no 0)
One thing to remember is that all nodes must be able to read from and write to the controlfile. CGS makes sure that members are valid, it uses a voting mechanism to check the validity of each member. I have already discussed the voting disk in my architecture section, as stated above memberships is held in a bitmap in the GRD, the CKPT process updates the controlfile every 3 seconds in an operation known as a heartbeat. It writes into a single block that is unique for each instance, thus intra-instance coordination is not required, this block is called the checkpoint progress record. You can see the controlfile records using the gv$controlfile_record_section view, all members attempt to obtain a lock on the controlfile record for updating, the instance that obtains the lock tallies the votes from all members, the group membership must conform to the decided (voted) membership before allowing the GCS/GES reconfiguration to proceed, the controlfile vote result is stored in the same block as the heartbeat in the control file checkpoint progress record.
A cluster reconfiguration is performed using 7 steps
1. Name service is frozen, the CGS contains an internal database of all the members/instances in the cluster with all their configurations and servicing details.
2. Lock database (IDLM) is frozen, this prevents processes from obtaining locks on resources that were mastered by the departing/dead instance
3. Determination of membership and validation and IMR
4. Bitmap rebuild takes place, instance name and uniqueness verification, GCS must synchronize the cluster to be sure that all members get the reconfiguration event and that they all see the same bitmap.
5. Delete all dead instance entries and republish all names newly configured
6. Unfreeze and release name service for use
7. Hand over reconfiguration to GES/GCS
Debugging CRS and GSD
Oracle server management configuration tools include a diagnostic and tracing facility for verbose output for SRVCTL, GSD, GSDCTL or SRVCONFIG.
To capture diagnose following the below
1. use vi to edit the gsd.sh/srvctl/srvconfig file in the $ORACLE_HOME/bin directory2. At the end of the file look for the below line
exec $JRE -classpath $CLASSPATH oracle.ops.mgmt.daemon.OPSMDaemon $MY_OHOME
3. Add the following just before the -classpath in the exec $JRE line
-DTRACING.ENABLED=true -DTRACING.LEVEL=2
4. the string should look like this
exec $JRE -DTRACING.ENABLED=true -DTRACING.LEVEL=2 -classpath...........
In Oracle database 10g setting the below variable accomplishes the same thing, set it to blank to remove the debugging
Enable tracing $ export SRVM_TRACE=true
Disable tracing $ export SRVM_TRACE=""
Adding or Deleting a Node
One of the jobs of a DBA is adding and removing nodes from a RAC environment when capacity demands, although you should add a node of a similar spec it is possible to add a node of a higher or lower spec.
The first stage is to configure the operating system and make sure any necessary drivers are installed, also make sure that the node can see the shared disks available to the existing RAC.
I am going to presume we have a two RAC environment already setup, and we are going to add a third node.
Pre-Install Checking
You used the Cluster Verification utility when installing the RAC environment, the tools check that the node has been properly prepared for a RAC deployment. You can run the command either from the new node or from any of the existing nodes in the cluster
pre-install check run from new node runcluvfy.sh stage -pre crsinst -n rac1,rac2,rac3 -r 10gr2
pre-install check run from existing node
cluvfy stage -pre crsinst -n rac1,rac2,rac3 -r 10g2
Make sure that you fix any highlighted problems before continuing.
Install CRS
Cluster Ready Services (CRS) should be installed first, this allows the node to become part of the cluster. Adding the new node can be started from any of the existing nodes
1. Log into any of the existing nodes as user oracle then run the below command, the script below starts the OUI GUI tool, hopefully the tool will already see the existing cluster and will fill in the details for you
$ORA_RS_HOME/oui/bin/addnode.sh
2. In the specify cluster nodes to add to installation screen, enter the new names for the public, private and virtual hosts
3. Click next to see a summary page
4. Click install, the installer will copy the files from the existing node to the new node. Once copied you will be asked to run orainstRoot.sh and root.sh as user root
5. Run orainstRoot.sh and root.sh in the new and rootaddnode.sh in the node that you are running the installation from.
orainstRoot.sh sets the Oracle inventory in the new node and set ownerships and permissions to the inventory
root.shchecks whether the Oracle CRS stack is already configured in the new node, creates /etc/oracle directory and adds the relevant OCR keys to the cluster registry and it adds the daemon to CRS and starts CRS in the new node.
rootaddnode.sh configures the OCR registry to include the new nodes as part of the cluster
6.
7. Click next to complete the installation. Now you need to configure Oracle Notification Services (ONS). The port can be identified by the below command
cat $ORA_CRS_HOME/opmn/conf/ons.config
8. Now run the ONS utility by supplying the <remote_port> number obtained above
racgons add_config rac3:<remote_port>
Installing Oracle DB Software
Once the CRS has been installed and the new node is in the cluster, it is time to install the Oracle DB software. Again you can use any of the existing nodes to install the software.
1. Log into any of the existing nodes as user oracle then run the below command, the script below starts the OUI GUI tool, hopefully the tool will already see the existing cluster and fill in the details for you
$ORA_RS_HOME/oui/bin/addnode.sh2. Click next on the welcome screen to open the specify cluster nodes to add to installation screen, you should have a list of all
the existing nodes in the cluster, select the new node and click next
3. Check the summary page then click install to start the installation
4. The files will be copied to the new node, the script will ask you to run run.sh on the new node, then click OK to finish off the installation
Configuring the Listener
Now its time to configure the listener in the new node
1. Login as user oracle, and set your DISPLAY environment variable, then start the Network Configuration Assistant
$ORACLE_HOME/bin/netca2. Choose cluster management
3. Choose listener
4. Choose add
5. Choose the the name as LISTENER
These steps will add a listener on rac3 as LISTENER_rac3
Create the Database Instance
Run the below to create the database instance on the new node
1. Login as oracle on the new node, set the environment to database home and then run the database creation assistant (DBCA)
$ORACLE_HOME/bin/dbca2. In the welcome screen choose oracle real application clusters database to create the instance and click next
3. Choose instance management and click next
4. Choose add instance and click next
5. Select RACDB (or whatever name you gave you RAC environment) as the database and enter the SYSDBA and password, click next
6. You should see a list of existing instances, click next and on the following screen enter ORARAC3 as the instance and choose RAC3 as the node name (substitute any of the above names for your environment naming convention)
7. The database instance will now created, click next in the database storage screen., choose yes when asked to extend ASM
Removing a Node
Removing a node is similar to above but in reverse order
1. Delete the instance on the node to be removed2. Clean up ASM
3. Remove the listener from the node to be removed
4. Remove the node from the database
5. Remove the node from the clusterware
You can delete the instance by using the database creation assistant (DBCA), invoke the program choose the RAC database, choose instance management and then choose delete instance, enter the sysdba user and password then choose the instance to delete.
To clean up ASM follow the below steps
1. From node 1 run the below command to stop ASM on the node to be removed
srvctl stop asm -n rac3 srvctl remove asm -n rac3
2. Now run the following on the node to be removed
cd $ORACLE_HOME/admin rm -rf +ASM cd $ORACLE_HOME/dbs rm -f *ASM*
3. Check that /etc/oratab file has no ASM entries, if so remove them
Now remove the listener for the node to be removed
1. Login as user oracle, and set your DISPLAY environment variable, then start the Network Configuration Assistant
$ORACLE_HOME/bin/netca2. Choose cluster management
3. Choose listener
4. Choose Remove
5. Choose the the name as LISTENER
Next we remove the node from the database
1. Run the below script from the node to be removed
cd $ORACLE_HOME/bin./runInstaller -updateNodeList ORACLE_HOME=$ORACLE_HOME "CLUSTER_NODES={rac3}" -local./runInstaller
2. Choose to deinstall products and select the dbhome
3. Run the following from node 1
cd $ORACLE_HOME/oui/bin ./runInstaller -updateNodeList ORACLE_HOME=$ORACLE_HOME "CLUSTER_NODES={rac1,rac2,rac3}"
Lastly we remove the clusterware software
1. Run the following from node 1, you obtain the port number from remoteport section in the ons.config file in $ORA_CRS_HOME/opmn/conf
$CRS_HOME/bin/racgons remove_config rac3:62002. Run the following from the node to be removed as user root
cd $CRS_HOME/install ./rootdelete.sh
3. Now run the following from node 1 as user root, obtain the node number first
$CRS_HOME/bin/olsnodes -n cd $CRS_HOME/install ./rootdeletenode.sh rac3,3
4. Now run the below from the node to be removed as user oracle
cd $CRS_HOME/oui/bin ./runInstaller -updateNodeList ORACLE_HOME=$ORACLE_HOME "CLUSTER_NODES={rac3}" CRS=TRUE -local ./runInstaller
5. Choose to deinstall software and remove the CRS_HOME
6. Run the following from node as user oracle
cd $CRS_HOME/oui/bin ./runInstaller -updateNodeList ORACLE_HOME=$ORACLE_HOME "CLUSTER_NODES={rac1,rac2,rac3}" CRS=TRUE
7. Check that the node has been removed, the first should report "invalid node", the second you should not see any output and the last command you should only see nodes rac1 and rac2
srvctl status nodeapps -n rac3 crs_stat |grep -i rac3 olsnodes -n