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Home -> Community -> Mailing Lists -> Oracle-L -> Antwort: RE: Buffer Busy Waits -- Sanity check please
Hi
I would try to set the table to cache mode. It seams that the blocks are
aged out from buffer - which is default for FTS.
alter table BBN_SRVvignette cache;
to avoid reloading into cache.
Ivo
Design & Development, Warehousemanagementsystems Dept.
KNAPP Systemsintegration GmbH
Waltenbachstraße 9
A-8700 Leoben, Austria
Phone: ++43/3842/805-0
e-Mail: ivo.libal_at_knapp-systems.com
"Thorns, Malcolm (NESL-IT)"
<Malcolm.Thorns_at_northern-elect An: Multiple recipients
of list ORACLE-L <ORACLE-L_at_fatcity.com>
ric.co.uk> Kopie:
Gesendet von: root_at_fatcity.com Thema: RE: Buffer Busy
Waits -- Sanity check please
11/27/2001 09:25 AM
Bitte antworten an ORACLE-L
Jeff,
The 3 sessions are doing the same (or similar) queries. In this case count(*) which is forcing a full table scan of the table in each session. The 3 sessions are thus trying to access the same blocks from the SGA, in the same order. Only 1 session can access a block in the SGA at a time - this is the session showing 'db file scattered read'. The other 2 sessions need to wait for the block (these waits show as 'buffer busy waits' - ie waiting for the block in the SGA). You will see the block id (and perhaps the file id) changing as the FTS's progress. Thus the sessions are 'chasing' each other through the blocks - holding each other up with SGA block contention - which shows up as 'buffer busy waits'. Hope that explains things.
Regards,
Malcolm
-----Original Message-----
Sent: Monday, November 26, 2001 11:21 PM
To: Multiple recipients of list ORACLE-L
We recently had a new website go live. Since then, I'm seeing constant
buffer busy waits
and after a period of time, I see sessions hung on the same block#. The
SQL query
is always a COUNT(*) (below). It's almost as though one session has a
lock
of some sort in the buffer cache and other sessions are blocked.
Although,
I've checked and
there's no DML ongoing, so I'm unsure as to why we would see this. Note
that v$session shows
78 and 393 to be INACTIVE, while 159 is ACTIVE. So it's like 159 can't
write to
the buffer cache because 78 and 393 have a lock there. Note that these
are
all defined
as persistent connections, via the Vignette front-end. I'm sure all the
clues are there
but my brain is too fuzzed to piece it together.
SID SQL_TEXT O/SUser
----- ----------------------------------------------------------------
SID EVENT P1TEXT P1 P2TEXT P2 P3TEXTP3
----- -------------------------- ------------ -- ----------- ------ ----- ------ 78 buffer busy waits file# 72 block# 109177 id 130 393 buffer busy waits file# 72 block# 109177 id 130 159 db file scattered read file# 72 block# 109177 blocks8
Email: thomasje_at_tce.com
DBA Quickplace: http://gkmqp.tce.com/tis_dba <http://gkmqp.tce.com/tis_dba>
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Thorns, Malcolm (NESL-IT) INET: Malcolm.Thorns_at_northern-electric.co.uk Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: Ivo.Libal_at_knapp-systems.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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 Tue Nov 27 2001 - 03:50:14 CST
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