Re: select for update wait issues

From: Mladen Gogala <mgogala_at_yahoo.com>
Date: Mon, 13 Apr 2015 17:30:10 -0400
Message-ID: <552C3562.6000000_at_yahoo.com>

On 04/13/2015 01:14 PM, Sandra Becker wrote:
> Several waits:
>
> EVENT ROW_CNT
> ----------------------------------- ----------------
> db file sequential read 7,714
> enq: PR - contention 551
> latch free 11,020
> log file sync 96,425
> read by other session 7,163
>

Sandra, how did you extract those wait events? What does the column ROW_CNT mean? The only meaningful value is the time spent waiting. You should extract the wait events from V$SESSION_EVENT table, for the session that is doing "SELECT FOR UPDATE". The meaning of the the wait events above is:

• Index read of a table
• Start process
• Latch free (cannot be described in more details without knowing which latch it is)
• Commit processing
• Self explanatory, probably related to latch waits.

If I was allowed to wild guess the problem, I would say that there is an index range scan where there hasn't been one before and that the table is frequently used, something like addresses, phones or ZIP codes.

-- 
Mladen Gogala
Oracle DBA
http://mgogala.freehostia.com

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Received on Mon Apr 13 2015 - 23:30:10 CEST