Hi Chao ,

I have checked the statstpack output regarding to this query , in raw
trace file i see lots of 'global cache cr request ' wait events but
the time they take is very little comparing to the disk read events:


select /*+NOPARALLEL(M) */count(*)
from
taniadm.MERKEZ_CIKIS_34 m

call count cpu elapsed disk query current
rows
------- ------ -------- ---------- ---------- ---------- ----------
----------
Parse 3 0.00 0.01 1 1 0
0
Execute 3 0.00 0.00 0 0 0
0
Fetch 3 61.10 767.28 307181 307209 0
3
------- ------ -------- ---------- ---------- ---------- ----------
----------
total 9 61.10 767.30 307182 307210 0
3

Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 46

Rows Row Source Operation
------- ---------------------------------------------------
1 SORT AGGREGATE (cr=102403 r=102399 w=0 time=262103077 us)
10133769 TABLE ACCESS FULL MERKEZ_CIKIS_34 (cr=102403 r=102399 w=0
time=257079273 us)


Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total
Waited
---------------------------------------- Waited ----------
------------
SQL*Net message to client 8 0.00
0.00
SQL*Net message from client 8 78.11
173.33
global cache cr request 154082 0.12
6.73
db file scattered read 23984 1.01
707.97
latch free 6 0.03
0.05
SQL*Net break/reset to client 2 0.00
0.00
library cache lock 4 0.00
0.00
db file sequential read 3 0.01
0.02
************************************************** *****************************

Here the total times waited value for global cache cr request is large
but total waited is very small . The majority of query time spent in
disk io.

For the direct/io , i have checked the oracle executables, straced
them (especially open system calls) and saw the o_direct flag , and :

filesystemio_options is set to none. (for ocfs i was told it was not
necessary to set it, since ocfs uses direct io without this parameter)


Kind Regrads,






"chao_ping" <zhuchao@gmail.com> wrote in message news:<1116479070.144515.220410@g47g2000cwa.googleg roups.com>...
> One possible reason could because of your global cache management. If
> you shutdown one node, maybe result will be diffirent.
>
> One question, is your OCFS doing directIO read? Else filesystem cache
> can mask your result.