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Thread: How to Speed Instance Recovery for RAC

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    Expert Oracle Administrator
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    Oct 2011
    New Delhi, India

    How to Speed Instance Recovery for RAC

    Use Recovery in Parallel by increasing the RECOVERY_PARALLELISM processes

    RECOVERY_PARALLELISM specifies the number of processes to participate in instance or crash recovery. A value of 0 or 1 indicates that recovery is to be performed serially by one process.The value cannot exceed PARALLEL_MAX_SERVERS

    Increase PARALLEL_EXECUTION_MESSAGE_SIZE for better recovery slave performance

    This specifies the upper limit for the size of parallel execution messages. The default will be specific to the operating system. The default value should be adequate for most applications. The max recommended value for this parameter is eight KB.
    Oracle sets this based on parallel_automatic_tuning. If this is TRUE, the default size is four KB. When parallel_automatic_tuning is set to FALSE, the setting will be slightly greater than two KB.

    Increase the size of the default Buffer Cache

    50% of the default buffer cache would be used for recovery buffers. If this is not enough, some of the steps of Instance recovery will be done in several passes.
    Wherever possible, I would allocate the Default Buffer Cache 50% additional memory space, compared to the allocation on a single Instance.


    During an instance recovery process, Oracle rolls back uncommitted transactions. Oracle can use fast-start parallel rollback to increase the efficiency of this recovery phase.

    When using fast-start parallel rollback, the background process SMON is used as a coordinator and rolls back sets of transactions in parallel, using multiple server processes. It is useful on systems where some transactions are longrunning and affects time required to rollback transactions following instance failure


    FALSE - Parallel rollback is disabled
    LOW - Limits the maximum degree of parallelism to 2 * CPU_COUNT
    HIGH - Limits the maximum degree of parallelism to 4 * CPU_COUNT

    Set an appropriate value for FAST_START_MTTR_TARGET

    The FAST_START_MTTR_TARGET parameter specifies the number of
    seconds that the database should take to perform crash recovery of a single
    instance. Setting this parameter specifies how aggressively you wish Oracle to
    perform background checkpoints during normal processing. Setting a lower value
    for this parameter will cause Oracle to perform more frequent background
    checkpoints. In the event of an instance failure, there will therefore be less redo
    to apply since the last checkpoint and consequently the time required to recover
    the transactions for the failed instance will be reduced.

    Use _FAST_START_INSTANCE_RECOVERY_TARGET to set the time instance recovery on RAC:
    The parameter is unsupported and undocumented and therefore you should contact Oracle Support before specifying a non-default value on a production database.
    _FAST_START_INSTANCE_RECOVERY_TARGET the target time for cluster availability in a
    RAC environment. This parameter determines the amount of the time for instance recovery.

    Additionally , Set these parameters should be set to enable parallelism :

    parallel_min_servers: This parameter is used at startup to specify for a single instance, the number of processes to be started for parallel operations. Set this to CPU_COUNT-1 to respawn recovery slaves at startup time.

    parallel_max_servers: This parameter specifies the maximum number of parallel execution processes and parallel recovery processes for an instance.

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