Re: Library Cache and Share wait on Latch - Version Count Huge
Date: Thu, 18 Mar 2010 08:34:12 +0800
Message-ID: <4602f23c1003171734v26ee29dcx9e1fa0793187eed7_at_mail.gmail.com>
Get rid of the histograms or change the CURSOR_SHARING away from SIMILAR (to FORCE for example if you need it).
There's a bug which number I don't remember where CURSOR_SHARING = SIMILAR combined with histograms will cause a huge amount of new child cursors to be generated. And the bad thing is, not even the V$SQL_SHARED_CURSOR shows what's wrong in 10g, in 11g they've added a new HASH_MATCH_FAILED condition for that.
I personally don't like cursor_sharing=*similar* anyway and also I don't like having histograms being created without my knowledge, so you should change your default METHOD_OPT from from AUTO to REPEAT, that way Oracle only refreshes these histograms which already have been created (by you) and doesn't create new ones based on its "clever" logic:
SQL> select dbms_stats.get_param('METHOD_OPT') from dual;
DBMS_STATS.GET_PARAM('METHOD_OPT')
FOR ALL COLUMNS SIZE *AUTO **<<--- better to set this to REPEAT*
Of course first you need to manually get rid of the histograms that were automatically created by the AUTO option...
-- Tanel Poder http://tech.e2sn.comReceived on Wed Mar 17 2010 - 19:34:12 CDT
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> Greetings. When I check the wait events recently for few days
> Library Cache and Share Pool wait got the very huge value.
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> When i check the V$SQLAREA few sql have very huge versions more than
> 3000.
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> My Database version is 10g Rel2 10.2.0.4 on Redhat Linux AS4 with
> update 4.
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> CURSOR_SHARING set to SIMILAR and OPTIMIZER_MODE=CHOOSE.
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> This is happening only recently and is it related to Automatic
> Statistics done on 10g Rel 2.
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> Please let me know how to check and avoid it.
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> Regards
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> Mudhalvan M.M
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