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Home -> Community -> Mailing Lists -> Oracle-L -> Re: sizing sort_area_size
Hi!
Just few additions about 9i's nice features for tuning sorts, hash joins & other work area operations:
SQL> select n.name,s.value
2 from v$statname n,v$sesstat s
3 where n.statistic#=s.statistic#
4 and n.name like '%workarea executions%'
5 and s.sid in (
6 select sid from v$session
7 where audsid=sys_context('USERENV','SESSIONID')
8 );
NAME VALUE ---------------------------------------------------------------- ---------- workarea executions - optimal 136 workarea executions - multipass 0 workarea executions - onepass 1
Optimal means in-memory work area operations (sorts, hash joins, bitmap merges, etc.), onepass & multipass mean on disk operations. In OLAP and reporting environments, on-disk sorting or hasing is often unavoidable, but you should try to keep your sorts away from multipass executions, this will heavily hit your TEMP TS IO (sort runs can't be merged in sort area in one run, several runs needed) also CPU (some data comparisions have to be done semi-redundantly). The larger your sort_area_size, the smaller is the chance you'll need multipass sorting. (v$sql_workarea_histograms table can be useful for finding optimal tradeoff between PGA memory usage and temp ts IO on system level. On session level, v$sql_ workarea and v$sql_workare_active contain very interesting statistics).
Tanel.
> The following query will give you an idea how to tune sort area size:
> 1 select n.name,s.value
> 2 from v$statname n,v$sesstat s
> 3 where n.statistic#=s.statistic#
> 4 and n.name like '%sort%'
> 5 and s.sid in (select sid from v$session
> 6* where audsid=sys_context('USERENV','SESSIONID'))
> SQL> /
>
> NAME
VALUE
> ---------------------------------------------------------------- ---------
-
> sorts (memory)
26
> sorts (disk)
0
> sorts (rows)
87
>
> SQL>
>
> --
> Mladen Gogala
> Oracle DBA
>
>
>
> > -----Original Message-----
> > From: ml-errors_at_fatcity.com [mailto:ml-errors_at_fatcity.com] On
> > Behalf Of rgaffuri_at_cox.net
> > Sent: Thursday, September 18, 2003 3:10 PM
> > To: Multiple recipients of list ORACLE-L
> > Subject: sizing sort_area_size
> >
> >
> > I have been doing some alter sessions to improve performance
> > of gigabyte sized 'minus' operations. How do I tell if this
> > is helping other than completion time?
> >
> > I believe that if LIOs to PIOs ratio improves with the SAME
> > query then sort_area_size has helped right?(notice Im not
> > trying to improve my cache/hit ratio).
> >
> > I get this from v$sess_io.
> >
> > how do I tell how much temp tablespace my session uses? I
> > cant find a statistic for it? I see that I used up all my PGA
> > since PGA size and PGA max size are equal in v$sesstat.
> >
> > anything else I can look at?
> >
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: <rgaffuri_at_cox.net
> > INET: rgaffuri_at_cox.net
> >
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> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Mladen Gogala
> INET: mladen_at_wangtrading.com
>
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> San Diego, California -- Mailing list and web hosting services
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Tanel Poder INET: tanel.poder.003_at_mail.ee Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Fri Sep 19 2003 - 11:54:41 CDT
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