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gcs log flush sync --wait event

原创 Linux操作系统 作者:howard_zhang 时间:2010-09-16 16:15:30 0 删除 编辑

 

在客户处AWR报告中发现TOP 5 EVENT出出现如下等待事件:

Event

Waits

Time(s)

Avg Wait(ms)

% Total Call Time

Wait Class

CPU time

 

4,989

 

96.6

 

gcs log flush sync

129,223

3,103

24

60.1

Other

reliable message

295

33

111

.6

Other

gc cr block busy

764

16

21

.3

Cluster

log file sync

10,132

8

1

.2

Commit

This is how it happens -

1)You fired an update statement on Instance-2.
2)However, the request for desired blocks was gone to Instance-1. So Instance-2 was
waiting on ''gc cr request'.
3)Instance-1 had the requested blocks but before it ships the blocks to Instance-2, it need to flush the changes from current block
to redo logs on disks. Until this is done Instance-2 waits on event - 'gcs log flush sync'.

The cause of this wait event 'gcs log flush sync' is mainly - Redo log IO performance.

To avoid this problem you need to =
1)Improve the Redo log I/o performance.
2) Set undersore parameter "_cr_server_log_flush" =false

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