High "gc" cluster wait with Warning: log write elapsed time

(Doc ID 2219204.1)

Last updated on APRIL 04, 2018

Applies to:

Oracle Database - Enterprise Edition - Version 11.2.0.4 and later
Information in this document applies to any platform.

Symptoms

For a short period of time, "gc" related waits show up in top in awr report:

Top 10 Foreground Events by Total Wait Time

Event Waits Total Wait Time (sec) Wait Avg(ms) % DB time Wait Class
gc buffer busy acquire 82,801 83.9K 1014 58.3 Cluster
gc cr block busy 5,376 31.2K 5799 21.7 Cluster
gc current block busy 4,020 13K 3225 9.0 Cluster
gc buffer busy release 61,783 8488.4 137 5.9 Cluster
enq: TX - index contention 13,960 4982.9 357 3.5 Concurrency
buffer busy waits 19,316 658 34 .5 Concurrency
enq: TX - row lock contention 62 626.8 10109 .4 Application

 

lgwr trace shows a small write took long time:

Warning: log write elapsed time 180002ms, size 24KB         ==>> a few minutes for the write to complete

 

ash also confirms all gc related waits started while the lgwr log writing was going on.



Cause

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