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.
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Friday, September 19, 2003 5:24 PM
> 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$session
> 6* where audsid=sys_context('USERENV','SESSIONID'))
> SQL> /
>
> NAME
VALUE
> ---------------------------------------------------------------- ---------
-
> sorts (memory)
26
> sorts (disk)
0
> sorts (rows)
87
>
> SQL>
>
> --
> Mladen Gogala
> Oracle DBA
>
>
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
> > Behalf Of [EMAIL PROTECTED]
> > Sent: Thursday, September 18, 2003 3:10 PM
> > To: Multiple recipients of list ORACLE-L
> > Subject: sizing sort_area_size
> >
> >
> > I have been doing some alter sessions to improve performance
> > of gigabyte sized 'minus' operations. How do I tell if this
> > is helping other than completion time?
> >
> > I believe that if LIOs to PIOs ratio improves with the SAME
> > query then sort_area_size has helped right?(notice Im not
> > trying to improve my cache/hit ratio).
> >
> > I get this from v$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: <[EMAIL PROTECTED]
> > INET: [EMAIL PROTECTED]
> >
> > Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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>
>
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> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Mladen Gogala
> INET: [EMAIL PROTECTED]
>
> Fat City Network Services -- 858-538-5051 http://www.fatcity.com
> 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: [EMAIL PROTECTED]
Fat City Network Services -- 858-538-5051 http://www.fatcity.com
San Diego, California -- Mailing list and web hosting services
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