V$INSTANCE_RECOVERY

V$INSTANCE_RECOVERY monitors the mechanisms available to users to limit recovery I/O. Those mechanisms are:

  • Set the LOG_CHECKPOINT_TIMEOUT initialization parameter

  • Set the LOG_CHECKPOINT_INTERVAL initialization parameter

  • Set the FAST_START_MTTR_TARGET initialization parameter

  • Set the size of the smallest redo log

Column Datatype Description
RECOVERY_ESTIMATED_IOS NUMBER Number of dirty buffers in the buffer cache. In the Standard Edition, this column is always null.
ACTUAL_REDO_BLKS NUMBER Current actual number of redo blocks required for recovery
TARGET_REDO_BLKS NUMBER Current target number of redo blocks that must be processed for recovery. This value is the minimum value of the following 3 columns, and identifies which of the 3 user-defined limits determines checkpointing.
LOG_FILE_SIZE_REDO_BLKS NUMBER Maximum number of redo blocks required to guarantee that a log switch does not occur before the checkpoint completes.
LOG_CHKPT_TIMEOUT_REDO_BLKS NUMBER Number of redo blocks that need to be processed during recovery to satisfy the LOG_CHECKPOINT_TIMEOUT parameter. The value displayed is not meaningful unless that parameter has been set.
LOG_CHKPT_INTERVAL_REDO_BLKS NUMBER Number of redo blocks that need to be processed during recovery to satisfy the LOG_CHECKPOINT_INTERVAL parameter. The value displayed is not meaningful unless that parameter has been set.
FAST_START_IO_TARGET_REDO_BLKS NUMBER This column is obsolete and maintained for backward compatibility. The value of this column is always null.
TARGET_MTTR NUMBER Effective MTTR (mean time to recover) target value in seconds. The TARGET_MTTR value is calculated based on the value of the FAST_START_MTTR_TARGET parameter (the TARGET_MTTR value is used internally), and is usually an approximation of the parameter's value. However, if the FAST_START_MTTR_TARGET parameter value is very small (for example, one second), or very large (for example, 3600 seconds), the calculation will produce a target value dictated by system limitations. In such cases, the TARGET_MTTR value will be the shortest calculated time, or the longest calculated time that recovery is expected to take.

If FAST_START_MTTR_TARGET is not specified, the value of this field is the current estimated MTTR.
ESTIMATED_MTTR NUMBER Current estimated mean time to recover (MTTR) based on the number of dirty buffers and log blocks (0 if FAST_START_MTTR_TARGET is not specified). Basically, this value tells you how long you could expect recovery to take based on the work your system is doing right now.
CKPT_BLOCK_WRITES NUMBER Number of blocks written by checkpoint writes
OPTIMAL_LOGFILE_SIZE NUMBER Redo log file size (in megabytes) that is considered optimal based on the current setting of FAST_START_MTTR_TARGET. It is recommended that the user configure all online redo logs to be at least this value. Note that redo log files must be at least 4 megabytes in size; otherwise an error is generated.
ESTD_CLUSTER_AVAILABLE_TIME NUMBER Estimated time (in seconds) that the cluster would become partially available should this instance fail. This column is only meaningful in an Oracle Real Application Clusters (Oracle RAC) environment. In a non-Oracle RAC environment, the value of this column is null.
WRITES_MTTR NUMBER Number of writes driven by the FAST_START_MTTR_TARGET initialization parameter
WRITES_LOGFILE_SIZE NUMBER Number of writes driven by the smallest redo log file size
WRITES_LOG_CHECKPOINT_SETTINGS NUMBER Number of writes driven by the LOG_CHECKPOINT_INTERVAL or LOG_CHECKPOINT_TIMEOUT initialization parameter
WRITES_OTHER_SETTINGS NUMBER Number of writes driven by other reasons (such as the deprecated FAST_START_IO_TARGET initialization parameter)
WRITES_AUTOTUNE NUMBER Number of writes due to auto-tune checkpointing
WRITES_FULL_THREAD_CKPT NUMBER Number of writes due to full thread checkpoints

See Also: