RE: SQL Tuning
Date: Mon, 2 May 2016 10:54:27 +0000
Message-ID: <CE70217733273F49A8A162EE074F64D9282D0C4A_at_EXMBX01.thus.corp>
Niall,
Given there are only 68K consistent gets for 31K blocks read I think that some of the disk count must be from a tablescan or index fast full scan - which might make the average seem less wonderful. Can't argue with the "check the wait summary", though, for a quick check. Better still, the plan headed Rowsource Operations" should show the time, disk and CR buffer gets accumulated - so easy to see exactly where most of the time went.
Regards
Jonathan Lewis
From: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] on behalf of Niall Litchfield [niall.litchfield_at_gmail.com] Sent: 02 May 2016 09:51
To: Jack van Zanen
Cc: oracle-l_at_freelists.org
Subject: Re: SQL Tuning
Jack
The "slow" query does 30k disk accesses, the "fast" one 0. If the plans really are identical then you've likely got your explanation right there. I would personally want to doublecheck the summary wait information that TKPROF can produce as well looks like you've got about 60s of wait time which would equate to an average i/o time of 2ms which is actually pretty good (for disk).
On Mon, May 2, 2016 at 5:14 AM, Jack van Zanen <jack_at_vanzanen.com<mailto:jack_at_vanzanen.com>> wrote: Hi All,
I have two identical databases as far as versions, datasize OS etc is concerned and have a query that produces an identical execution plan. However this part of the 10046 trace is significantly different.
The slow query is on test (first listing) and is severely constricted in its memory so my explanation would be that the tables involved are actually in the buffer cache in prod (second listing) where the sga is much larger and therefore no disk I/O is required.
I will be having a look at the buffer cache next to check what is in there
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.01 0 0 0 0 Execute 1 0.01 0.22 0 0 0 0 Fetch 1 3.74 65.97 30927 68453 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 3 3.76 66.21 30927 68453 0 0 call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.02 0 8 0 0 Execute 1 0.01 0.01 0 83 0 0 Fetch 1 0.32 0.53 0 68507 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 3 0.34 0.57 0 68598 0 0
Jack van Zanen
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Niall Litchfield
Oracle DBA
http://www.orawin.info
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Received on Mon May 02 2016 - 12:54:27 CEST