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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Very high buffer gets
No. of blocks as seen from dba_segments:
SEGMENT_NAME SEGMENT_TYPE BLOCKS ------------------------------ ------------------ ---------- AQ$_QUEUE_TABLES TABLE 15 AQ$_QUEUES TABLE 15 AQ$_QUEUE_TABLE_AFFINITIES TABLE 15 ________________________________
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Joseph Amalraj
Sent: Tuesday, February 14, 2006 11:34 AM
To: oracle-l_at_freelists.org
Subject: RE: Very high buffer gets
Can you tell, what is the blocks
from dba_segments
for these segments.
Thanks
"Nahata, Naveen (US - Glen Mills)" <nnahata_at_deloitte.com> wrote:
I did a full compute, see below:
1 select blocks, num_rows, sample_size, to_char(last_analyzed, 'DD-MON-YYYY HH24:MI:SS')
2 from all_tables
3* where table_name in ('AQ$_QUEUE_TABLES',
'AQ$_QUEUE_TABLE_AFFINITIES', 'AQ$_QUEUES')
SQL> set lines 100
SQL> /
BLOCKS NUM_ROWS SAMPLE_SIZE TO_CHAR(LAST_ANALYZED,'DD-
---------- ---------- ----------- --------------------------
1 61 61 06-FEB-2006 15:50:09
2 136 136 06-FEB-2006 15:51:14
1 61 61 06-FEB-2006 15:50:48
I figured out with the help of John Clarke, that there are too
many CR blocks being read, but I still fail to understand why 645 blocks
/ row?
Am going to do a 10201 trace alongwith 10046 trace to figure out what's going on.
Naveen
2006/2/13, Nahata, Naveen (US - Glen Mills) <nnahata_at_deloitte.com>:
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$_AQERROR') and t.schema =locked
'SYSTEM')for update of
t.name <http://t.name/> , aft.table_objno skip
call count cpu elapsed disk query current
rows ------- ------ -------- ---------- ---------- ---------- ---------- ---------- Parse 84 0.00 0.03 0 0 0 0 Execute 84 0.03 0.03 0 0 0 0 Fetch 84 11.87 47.87 266 536288 45281 4627 ------- ------ -------- ---------- ---------- ---------- ---------- ---------- total 252 11.90 47.94 266 536288 45281 4627 Misses in library cache during parse: 1 Optimizer goal: CHOOSE Parsing user id: SYS (recursive depth: 1) Rows Row Source Operation ------- --------------------------------------------------- 60 FOR UPDATE 62 HASH JOIN 59 NESTED LOOPS 59 TABLE ACCESS FULL AQ$_QUEUE_TABLES 59 TABLE ACCESS BY INDEX ROWID AQ$_QUEUE_TABLE_AFFINITIES 59 INDEX UNIQUE SCAN AQ$_QTABLE_AFFINITIES_PK (object id 2400) 64 TAB LE ACCESS FULL AQ$_QUEUES Naveen
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-- http://www.freelists.org/webpage/oracle-lReceived on Wed Feb 15 2006 - 07:53:56 CST
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