今天检查一个数据库时发现有很多关于log的大量等待如下：
log file parallel write
log file sync
log buffer space
查询相关资料得到关于这些事件的详细叙述：
log buffer space
Waiting for space in the log buffer because the session is writing data into the log buffer faster than LGWR can write it out. Consider making the log buffer bigger if it is small, or moving the log files to faster disks such as striped disks.
Wait Time: Usually 1 second, but 5 seconds if it is waiting for a Switch Logfile to complete
Parameters: None
log file parallel write
Writing redo records to the redo log files from the log buffer.
Wait Time: Time it takes for the I/Os to complete. Even though redo records are written in parallel, the parallel write is not complete until the last I/O is on disk.
| Parameter | Description |
|---|---|
| files | Number of files to be written |
| blocks | Number of blocks to be written |
| requests | Number of I/O requests |
log file sync
When a user session commits, the session's redo information needs to be flushed to the redo logfile. The user session will post the LGWR to write the log buffer to the redo log file. When the LGWR has finished writing, it will post the user session.
Wait Time: The wait time includes the writing of the log buffer and the post.
| Parameter | Description |
|---|---|
| buffer# | The number of the physical buffer in the redo log buffer that needs to be synchronized |
---------- ------- ------- ------------------------------------------------------------ ---
1 ONLINE /ora/u02/oradata/cudwh01/cudwh01_redo_1a.log NO
1 ONLINE /ora/u04/oradata/cudwh01/cudwh01_redo_1b.log NO
1 ONLINE /ora/u04/oradata/cudwh01/cudwh01_redo_1c.log NO
4 ONLINE /ora/u02/oradata/cudwh01/cudwh01_redo_4a.log NO
4 ONLINE /ora/u04/oradata/cudwh01/cudwh01_redo_4b.log NO
4 ONLINE /ora/u05/oradata/cudwh01/cudwh01_redo_4c.log NO
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ------------ ------------ ------------
1 1 52359 209715200 512 3 NO ACTIVE 1.1527E+10 20-JUL-11 1.1527E+10 20-JUL-11
4 1 52360 209715200 512 3 NO CURRENT 1.1527E+10 20-JUL-11 2.8147E+14
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/674865/viewspace-702614/ ，如需转载，请注明出处，否则将追究法律责任。
