Статистики REDO из представлений V$SESSTAT and V$SYSSTAT

dbstalker, 23 марта

Очень немного о статистиках и запросов с ними.

redo buffer allocation retries Total number of retries necessary to allocate space in the redo buffer. Retries are needed either because the redo writer has fallen behind or because an event such as a log switch is occurring.

redo entries Number of times a redo entry is copied into the redo log buffer

Дополнительно на эту тему здесь.

redo blocks written Total number of redo blocks written. This statistic divided by "redo writes" equals number of blocks per write.

redo wastage Number of bytes wasted because redo blocks needed to be written before they are completely full. Early writing may be needed to commit transactions, to be able to write a database buffer, or to switch logs.

Дополнительно можно здесь посмотреть.

redo log space requests Number of times the active log file is full and Oracle must wait for disk space to be allocated for the redo log entries. Such space is created by performing a log switch. Log files that are small in relation to the size of the SGA or the commit rate of the work load can cause problems. When the log switch occurs, Oracle must ensure that all committed dirty buffers are written to disk before switching to a new log file. If you have a large SGA full of dirty buffers and small redo log files, a log switch must wait for DBWR to write dirty buffers to disk before continuing. Also examine the log file space and log file space switch wait events in V$SESSION_WAIT Подробнее смотрите здесь.

redo log space wait time Total elapsed waiting time for "redo log space requests" in 10s of milliseconds. If this value for redo log space wait time is low, your log buffer size (log_buffer) is sized properly.

redo log switch interrupts Number of times that another instance asked this instance to advance to the next log file

redo ordering marks Number of times that a system change number was allocated to force a redo record to have an higher SCN than a record generated in another thread using the same block

redo size Total amount of redo generated in bytes (размер журнальной информации)

redo write time Total elapsed time of the write from the redo log buffer to the current redo log file in 10s of milliseconds

redo writer latching time Elapsed time in 10s of milliseconds needed by LGWR to obtain and release each copy latch

redo writes Total number of writes by LGWR to the redo log files. "redo blocks written" divided by this statistic equals the number of blocks per write



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