RE: Very high buffer gets
- From: "Nahata, Naveen (US - Glen Mills)" <nnahata@xxxxxxxxxxxx>
- To: <joseph@xxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 15 Feb 2006 08:53:56 -0500
No. of blocks as seen from dba_segments:
SEGMENT_NAME SEGMENT_TYPE BLOCKS
------------------------------ ------------------ ----------
AQ$_QUEUE_TABLES TABLE 15
AQ$_QUEUES TABLE 15
AQ$_QUEUE_TABLE_AFFINITIES TABLE 15
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Joseph Amalraj
Sent: Tuesday, February 14, 2006 11:34 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Very high buffer gets
Can you tell, what is the blocks
from dba_segments
for these segments.
Thanks
"Nahata, Naveen (US - Glen Mills)" <nnahata@xxxxxxxxxxxx> wrote:
I did a full compute, see below:
1 select blocks, num_rows, sample_size,
to_char(last_analyzed, 'DD-MON-YYYY HH24:MI:SS')
2 from all_tables
3* where table_name in ('AQ$_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@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 TAB LE ACCESS FULL AQ$_QUEUES
Naveen
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