RE: Very high buffer gets
- From: "Nahata, Naveen (US - Glen Mills)" <nnahata@xxxxxxxxxxxx>
- To: "fairlie rego" <fairlie_r@xxxxxxxxx>
- Date: Tue, 14 Feb 2006 08:34:49 -0500
Yes, I have already seen this note. Ultimately, I will go ahead with
what is recommended in the metalink note, but I fail to understand why
too many blocks are being read and hence posted the query in this forum.
Probably its because of my lack of experience with AQ/IOTs I cannot come
up with a reasonable explanation.
Naveen
________________________________
From: fairlie rego [mailto:fairlie_r@xxxxxxxxx]
Sent: Monday, February 13, 2006 7:22 PM
To: Nahata, Naveen (US - Glen Mills)
Cc: oracle-l@xxxxxxxxxxxxx; Alex Gorbachev
Subject: RE: Very high buffer gets
Hi Naveen
Isn't this the same issue as described in Metalink note 310923.1
<https://www.metalink.oracle.com/metalink/plsql/f?p=130:14:4200270662525
378742::::p14_database_id,p14_docid,p14_show_header,p14_show_help,p14_bl
ack_frame,p14_font:NOT,310923.1,1,1,1,helvetica>
Regards,
Fairlie
"Nahata, Naveen (US - Glen Mills)" <nnahata@xxxxxxxxxxxx> wrote:
9.2.0.6 (on HP-UX)
________________________________
From: Alex Gorbachev [mailto:gorbyx@xxxxxxxxx]
Sent: Monday, February 13, 2006 4:07 PM
To: Nahata, Naveen (US - Glen Mills)
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: Very high buffer gets
If I recall correctly this is a bug in AQ handling. I think you
should be able to find it easilly on Metalink. I think Oracle attributes
LIO that is caused by QMN during queue maintenance (delayed purging)
instead of attributing those LIOs to the statements causing it. What is
your version?
2006/2/13, Nahata, Naveen (US - Glen Mills)
<nnahata@xxxxxxxxxxxx>:
Hi All,
After tracing the QMON process which was doing lots of
buffer gets, I
found this culprit. None of the three tables involved in
the query have
more than 2 blocks. I know the nested loop is iterating
over the blocks
but that should still not account for more than 200
blocks / execution.
Why do I see such high values for buffer gets?
select t.schema , t.name <http://t.name/> , t.flags,
q.name <http://q.name/>
from
system.aq$_queue_tables t,
sys.aq$_queue_table_affinities aft,
system.aq$_queues q where aft.table_objno = t.objno and
aft.owner_instance =
:1 and q.table_objno = t.objno and q.usage = 0
and
bitand(t.flags, 4+16+32+64+128+256) = 0 and NOT
( t.name <http://t.name/>
in
('DEF$_AQCALL' , 'DEF$_AQERROR') and t.schema =
'SYSTEM')for update of
t.name <http://t.name/> , aft.table_objno skip locked
call count cpu elapsed disk
query current
rows
------- ------ -------- ---------- ----------
---------- ----------
----------
Parse 84 0.00 0.03 0
0 0
0
Execute 84 0.03 0.03 0
0 0
0
Fetch 84 11.87 47.87 266
536288 45281
4627
------- ------ -------- ---------- ----------
---------- ----------
----------
total 252 11.90 47.94 266
536288 45281
4627
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: SYS (recursive depth: 1)
Rows Row Source Operation
-------
---------------------------------------------------
60 FOR UPDATE
62 HASH JOIN
59 NESTED LOOPS
59 TABLE ACCESS FULL AQ$_QUEUE_TABLES
59 TABLE ACCESS BY INDEX ROWID
AQ$_QUEUE_TABLE_AFFINITIES
59 INDEX UNIQUE SCAN AQ$_QTABLE_AFFINITIES_PK
(object id 2400)
64 TABLE ACCESS FULL AQ$_QUEUES
Naveen
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Best regards,
Alex Gorbachev
Fairlie Rego
Senior Oracle Consultant
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