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log file sync等待事件

原创 Linux操作系统 作者:xxet1034 时间:2012-07-05 09:43:16 0 删除 编辑
log file sync 官方文档解释:
When a user session commits (or rolls back), the session's redo information must be flushed to the redo logfile by LGWR. The server process performing the COMMIT or ROLLBACK waits under this event for the write to the redo log to complete.
如果avg time低,并且等待次数多,就说明有可能应用程序的dml操作后的commit或者rollback频繁,比如一次insert,一次commit,这种情况就可以采用批量提交的方式来降低此等待。
如果avg time高,就要看它在做什么上花费了大量此等待,如果是因为io的原因,那么:
  • Reduce other I/O activity on the disks containing the redo logs, or use dedicated disks.

  • Alternate redo logs on different disks to minimize the effect of the archiver on the log writer.

  • Move the redo logs to faster disks or a faster I/O subsystem (for example, switch from RAID 5 to RAID 1).

  • Consider using raw devices (or simulated raw devices provided by disk vendors) to speed up the writes.

  • Depending on the type of application, it might be possible to batch COMMITs by committing every N rows, rather than every row, so that fewer log file syncs are needed.

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