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This column is obsolete and maintained for backward compatibility.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 |
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. |
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:
Oracle Database Performance Tuning Guide for more information on limiting recovery I/O, and how Oracle determines MTTR recovery times