Understand oracle real application cluster

Oracle Real Application ClusterSatishbabu Gunukula12+ Years of Experience in Oracle, SQLServer Database TechnologiesOracle Certified Professional Oracle 8i,9i,10gOracle Certified Expert Oracle 10g RAChttp://www.oracleracexpert.com

Objective• What is Real Application Cluster?• Oracle Cluster Benefits & Components• Oracle Cluster Ready Services• Interconnect & Cache fusion• Oracle RAC Database & ASM• Transparent Application Failover (TAF)• Backup & Recovery• New Features in Oracle 11g RAC

What is Real Application Cluster• Lower Cost• Scalability• High Availability• Ease Of Administration• Transparent to users• GRID computing• More than one instance per database.• Instances are running on different nodes.• Instances on different nodes writes to the same physical Database

What is Real Application Cluster• Control file, Data files, Temp Files and Spfiles are on a shared storage• Shared storage may have a Clustered file system or ASM or Raw Volumes• Every Instance will have its own redo log files and Undo segments• Every Instance has its own background process• All Cache (Data Buffer,Library ,Data Dictionary ) are synchronized by Cache Fusion and resources managed globally• Backup and Recovery databases from any instance in the Cluster.

What is Real Application Cluster• Sessions failover using Transparent Application Failover (TAF)• Users can connect to any active instance (load balance)• Additional waits due to interconnect traffic Node1 Node2 Instance 1 Instance 2 Archived Logs Archived Logs (Local Storage) (Local Storage) Undo Tablespace Data Files Undo Tables pace for Instance 1 Temp Files for Instance 2 Control Files Online Redo log Flash Recovery AreaFiles Online Redo log files for Instance 1 Change Tracking File files for Instance2 Spfile Shared Storage

Shared StorageShared store is very critical component in Oracle RAC. BothSAN/NAS are supported.• Supported file storage - Raw volumes - Cluster File system(Oracle ACFS,OCFS,OCFS2) - Oracle ASM (Automatic Storage Management) - Direct NFS (new feature in 11g)• Physical Connections to shared storage - Fully redundant active –active IO paths• For iSCSI - Fully redundant IO paths for iSCSI with multiple NIC card each server and Gigabit Ethernet switches.

Shared Storage

Oracle Clusterware• Oracle Clusterware enables servers to communicate with each other• Each server in cluster has addition processes that communicate with other servers.• Oracle clusterware manages the resources, such as Virtual IP Addresses, Instances, databases, listeners, services..etc.• You can also use Oracle Clusterware to manage the user applications.

Benefits of using Cluster• Scalability of Applications• Use of less expensive commodity hardware• Ability of failover• Ability to program the startup of applications in planned order• Ability to monitor processes• Ability to restart the process if they stop• Ability to increase capacity over time by adding servers

Oracle Clusterware Benefits• Eliminate unplanned downtime• Reduce or eliminate planned downtime for maintenance• Increase throughput by enabling applications to run on all the nodes in a cluster• Increase the throughput on demand for clustware applications by adding serves• Reduce the total cost for infrastructure

Oracle clusterware components• Software components  Voting Disk- Oracle clusterware uses this component to determine the which nodes are members of a cluster  Oracle Cluster Registry(OCR) – Oracle clusterware uses OCR to sore and mange information about high-availability components in the cluster, such as cluster node list, cluster database instance to node mapping, VIP address, services and applications.• Both Vote and OCR must reside on shared storage that is accessible by all nodes in a cluster• At least 3 voting disks and maximum of 15 disks• To ensure high availability multiplex OCR location up to 5 locations

Oracle clusterware Network Config• The VIP addresses must be resolved by the clients. The (Grid Naming Service) GNS is linked to the corporate Domain Name Service (DNS) so that clients can easily connect to the cluster and the databases running there• Single Client Access Name (SCAN) - The SCAN is a single name that resolves to three IP addresses in the public network. When using GNS and DHCP, Oracle Clusterware configures the VIP addresses for the SCAN name that is provided during cluster configuration• Oracle 11g R2 supports the use of DHCP for all private interconnect addresses, as well as for most of the VIP addresses.

Interconnects• Cluster Interconnect is very important private network used for communication between all other nodes• Network pings are performed by Cluster Synchronization Services (ocssd.bin)• Connected via switch to other nodes• New wait events due to traffic over interconnect• Enhanced technology has helped Cache Fusion• You can use OS dependent methods like Bonding on Unix and teaming on Windows• OS independent redundant interconnect available from 11.2.0.2 onwards (Not on Windows)

Cache Fusion• Cache coherency is the technique used to keep multiple copies of a block consistent between different oracle instance.• GCS implements the cache coherency by using Cache fusion algorithm• GES maintains all non-cache fusion resource operations• Cache Fusion addresses several types of concurrency as below: – Concurrent Reads on Multiple Nodes – Concurrent Reads and Writes on Different Nodes – Concurrent Writes on Different Nodes• Cache Fusion partially implemented in Oracle 8i OPS

Cache Fusion• Request a block for a Modification1. Instance1 submits a request to GCS to modify the block.2. The GCS transmits the request to the holder, i.e. instance 23. Instance 2 receives the request message and the LMS process sends the block to instance 1.4. On receipt of the block, instance 1 informs the GCS that it holds the block in exclusive mode

Cache Fusion• Write a Block to Disk1. Instance2 sends a request to GCS to write block to disk2. The GCS forwards the request to instance 13. Instance 1 receives the request and writes the block to disk.4. Instance 1 notifies the write operation to GCS5. After receipt of notification GCS orders PI holders to discard their PI’s

Block Access and Buffer states• To see a buffers state, query the STATUS column of the V$BH dynamic performance view.• Block access mode - NULL and buffer state name – CR – An instance can perform a consistent read of the block. That is, if the instance holds an older version of the data.• Block access mode -S and buffer state name – SCUR – An instance has shared access to the block and can only perform reads.• Block access mode - X and buffer state name – XCUR – An instance has exclusive access to the block and can modify it.• Block access mode - NULL and buffer state name is – PI – An instance has made changes to the block but retains copies of it as past images to record its state before changes.

Block Access and Buffer states• SCUR and PI buffer states are RAC specific• There can be only one copy of any one block buffered in the XCUR state• To perform modifications on a block, a process must assign an XCUR buffer state to the buffer containing the data block.

Cluster ready servicesBelow processes must run after CRS installation In order forCluster Ready Services to function• evmd -- Event manager daemon that starts the racgevt process to manage callouts.• ocssd -- Manages cluster node membership and runs as oracle user; failure of this process results in cluster restart.• crsd -- Performs high availability recovery and management operations such as maintaining the OCR. Also manages application resources and runs as root user and restarts automatically upon failure.

Oracle Clusterware Stack

Cluster ready service Stack• Cluster Ready Services (CRS): For managing high availability operations in a cluster.• Cluster Synchronization Services (CSS): Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster.• Automatic Storage Management (ASM): Provides disk management for Oracle Clusterware.• Cluster Time Synchronization Service (CTSS): Provides time management in a cluster for Oracle Clusterware.• Event Management (EVM): A background process that publishes events that Oracle Clusterware creates.

Cluster ready service Stack• Oracle Notification Service (ONS): Publish and subscribes service for communicating Fast Application Notification (FAN) events.• Oracle Agent (oraagent): To support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur. This process was known as RACG in Oracle11g R1• Oracle Root Agent (orarootagent): oraagent process that helps crsd to manage resources owned by root, such as the network, and the Grid virtual IP address

High Availability Services Stack• Grid Plug and Play (gpnpd): Provides access to the Grid Plug and Play profile, and coordinates updates to the profile among the nodes of the cluster to ensure that all of the nodes node have the most recent profile.• Grid Interprocess Communication (GIPC): A helper daemon for communications infrastructure. Currently has no functionality; to be activated in a later release.• Multicast Domain Name Service (mDNS): Allows DNS requests. The mDNS process is a background process on Linux and UNIX, and a service on Windows.• Oracle Grid Naming Service (GNS): A gateway between the cluster mDNS and external DNS servers. The gnsd process performs name resolution within the cluster.

RAC Database• Use DBCA (Database Configuration Assistant) to create database and you can also configure listeners and Enterprise Manager• Before you create Database – The Oracle Cluster Ready services must be installed and configured. Share disk must be in place. – If planning to use ASM then ASM resources should be available. – Oracle Database software must be installed• DBCA Automatically recognized the cluster environment and will provide the options of configuring the RAC environment.• If database created manually then use srvctl to register the database in the OCR

RAC Specific Background Processes• LMON: Global Enque Service Monitor – Maintains instance membership within Oracle RAC. – All non-cache fusion interinstance resource operations – The process detects instance transitions and performs reconfiguration of GES and GCS resources.• LMD: Global Enque Service Demon – Manages incoming enqueue request messages and controls access to global enqueues. – It also performs distributed deadlock detections• Global Cache Service and Global enqueue service manages Global Resource Directory (GRD)

RAC Specific Background Processes• LMSx: Global Cache Service Processes, where x can be 0 to 10 – Managing the resource requests and cross-instance call operation – block transfers and other GCS-related messages• LCKx: Lock processes – This process manages the global enqueue requests and the cross-instance broadcast• DIAG : Diagnosability process – Monitors the health of the instance and captures the data for process failures

Automatic Storage Management(ASM) • ASM provides portable and high performance database file system and simplifies database administration • ASM spread data across the disks and distributes I/O load across all available resources to optimize performance • ASM provides integrated mirroring across disks • Dynamically add the space without shutdown of the database • It is advised to use separate ORACLE_HOME for ASM install • You can configure the ASM using DBCA • A separate instance (ASM) starts in order to manage ASM disks, resources and connectivity • Both ASM and Database instances have access to common set of disks called disk groups

ASM background processesASM background Process• ARBn : Performs the actual rebalance data extent movements in an Automatic Storage Management instance. More than one process can run at a time, named ARB0, ARB1, and so on.• ASMB : Runs in a database instance that is using an ASM disk group and communicates with the ASM instance in managing storage and providing statistics.• GMON: Maintains disk membership in ASM disk groups.• MARK: This process marks ASM allocation units as stale following a missed write to an offline disk. This essentially tracks which extents require resync for offline disks.• RBAL: This process runs in both database and ASM instances. In the database instance, it does a global open of ASM disks and in an ASM instance, it also coordinates rebalance activity for disk groups

New initialization parametersUnique parameters in RAC Instance• instance_name- Specifies the unique name of this instance• instance_number- Specifies the unique number that maps to instance• thread – Specifies the number of the redo thread used by the instanceNon-Unique parameters in RAC Instance• cluster_database – specifies weather RAC enabled or not• cluster_database_instance – equal to the number of instances in a cluster• cluster_interconnects – Specifies the additional interconnects available for use• active_instance_count– specifies the number of instances that will be active within a cluster

New parameters• remote_listener -specifies a network name that resolves to an address or address list of Oracle Net remote listeners• local_listener - specifies a network name that resolves to an address or address list of Oracle Net local listenersParameters in ASM Instance• instance_type – This parameter must be set to ASM• asm_diskgroups – lists the name of the disk groups that will be mounted by ASM instance• asm_diskstring – This parameter limits the set of disks that ASM consider for discovery• asm_power_limit – specifies the Maximum power on an ASN instance for disk rebalance operations• asm_preferred_read_failure_groups - specifies the failure groups that contain preferred read disks

Transparent Application Failover(TAF)• Transparent Application Failover (TAF) is a client-side feature that allows for clients to reconnect to surviving nodes in the event of a failure of an instance.• The reconnect happens automatically from within the OCI (Oracle Call Interface) library. Any uncommitted transactions are rolled back and server side program variables and session properties will be lost.• In some case the select statements automatically re- executed on the new connection with the cursor positioned on the row on which it was positioned prior to the failover.• The failover is configured in tnsnames.ora file, the TAF settings are placed in CONNECT_DATA section of the tnsnames.ora using FAILOVER_MODES parameters

TAF failover & load balance methods• Failover modes - TYPE: TAF supports three types of failover types SESSION: If a users connection is lost, SESSION failover establishes a new session automatically created for the user on the backup node. This type of failover does not attempt to recover selects SELECT: If the connection is lost, Oracle Net establishes a connection to another node and re-executes the SELECT statements with cursor positioned on the row on which it was positioned prior to the failover NONE: This setting is the default and failover functionality is provided. Use this setting to prevent failover. - METHOD: This parameters determines how failover occurs from the primary node to the backup node BASIC: Use this mode to establish connections at failover time, no work on the backup server until failover time

TAF failover & load balance methods PRECONNECT: Use this mode to pre-established connections. - RETRIES: Use this parameter to specify number of times to attempt to connect after a failover - DELAY: Use this parameter to Specify the amount of time in seconds to wait between connect attempts.• LOAD_BALANCE:YES,NO,OFF,TRUE• There are two methods of load balancing - Client load balancing - Distributes new connections among Oracle RAC nodes so that no one server is overloaded with connection requests - Server load balancing – Distributes processing workload among RAC nodes and new user session connection requests to the least loaded listener.• For failover information query view GV$SESSION – failover_type,failover_method,failed_over

OCR & Vote Backup and Recovery• Oracle recommends that you back up your OCR & voting disk after initial cluster creation• OCR - There are two methods to backup OCR 1. Automatically generated OCR backup files under $CRS_HOME/cdata/crs 2. OCR export/logical backup # ocrconfig -export export_file_name• Use ocrconfig to restore OCR from backup # ocrconfig –restore $CRS_HOME/cdata/crs/day.ocr or # ocrconfig –import export_file_name• Vote –Use dd or ocopy command Backup - $ dd if=vote_disk_name of=backup_file_name Recovery- $ dd if=backup_file_name of=vote_disk_name

RAC Database Backup• Backup RAC Database from any node in a Cluster• You can take Full and incremental backup using RMAN• You can backup to Tape,Disk and Cloud (using Media Management Library from Oracle 11g)• You can use Flash Recovery Area(FRA) for your backups• As a Best practice, the backup device should be shared between the nodes for easy recovery• Perform backups of your RAC database using Enterprise Manager• Scale up the Backup load onto multiple Instances of RAC RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 2; RMAN> CONFIGURE CHANNEL C1 CONNECT ‘sys/xxxx@inst1’; RMAN> CONFIGURE CHANNEL C2 CONNECT ‘sys/xxx@Inst2’;

RAC Database Recovery• Automatic instance recovery occurs for failed instances due to hardware or software problems – SMON Determines the block needed for recovery and Global Resource Directory (GRD) is forgen – GES remasters enqueues and GCS remasters the resources – Buffer space for recovery allocated and block not in recovery will be accessible, oracle performs roll forward recovery.• As long as one instance survives, RAC performs instance recovery for any other failed instances• In case of any Media failure recovery the database from any instance in the Cluster. After recovery manually start the other instance in cluster.• If using Flashbak Recovery Area then you can SWTICH the database, in case of media recovery.

Performance tuning• ADDM (Automatic Database Diagnostic Monitor) is a performance monitor tool, which proactively monitors the performance and also captures RAC related issues• The statistical data needed for diagnosis of a problem is saved in the Automatic Workload Repository (AWR).• Oracle Database 10g uses a scheduled job, GATHER_STATS_JOB(GATHER_DATABASE_STATS_JOB_PROC ) to collect AWR statistics• The ADDM Analyzed the data in AWR on regular basis to find the root cause of performance problems and provides recommendations to correct the problems.• ADDM is enabled by default and is controlled by the STATISTICS_LEVEL initialization parameter. This parameter should be set to the TYPICAL or ALL to enable the ADDM, default setting is TYPICAL.• For ADDM Analysis you can run addmrpt.sql

Performance tuning• For AWR reports you can run awrrpt.sql, awrrpti.sql for RAC• ADDM provides the following benefits: – Automatic performance diagnostic report every hour by default – Problem diagnosis based on decades of tuning expertise – Time-based quantification of problem impacts and recommendation benefits – Identification of root cause, not symptoms – Recommendations for treating the root causes of problems – Identification of non-problem areas of the system – Minimal overhead to the system during the diagnostic process• The v$cache_transfer and v$file_cache_transfer views are used to examine RAC statistics

Performance tuning• In RAC, the global services directory processes is the most important tuning area. GSD is communicates through cluster interconnect. If cluster interconnects do not perform properly, the entire RAC will suffer no matter how well everything else is tuned.• The Global Enqueue Services (GES) and Global Cache Services (GCS) are the main process• Wait events can be divided as three categories – 1.Time-based event – 2.System-wide event – 3.Session wait• The major wait events in Oracle RAC are: – gc cr request – gc buffer busy

Performance tuning• The most important wait events for RAC include various categories, such as:• Block-oriented – gc current block 2-way – gc current block 3-way – gc cr block 2-way – gc cr block 3-way• Message-oriented – gc current grant 2-way – gc cr grant 2-way• Contention-oriented – gc current block busy – gc cr block busy – gc current buffer busy

Performance tuning• Load-oriented – gc current block congested – gc cr block congested

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Understand oracle real application cluster

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