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FAST_START_IO_TARGET_REDO_BLKS NUMBER This column is obsolete and maintained for backward compatibility.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 a Real Application Clusters (RAC) environment. In a non-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: