Re: Slower performance after enabling async io on Oracle Linux
Date: Wed, 16 May 2012 01:32:51 -0700 (PDT)
Message-ID: <32754071.248.1337157171649.JavaMail.geo-discussion-forums_at_vbyg17>
On Tuesday, May 15, 2012 8:05:53 PM UTC+2, Mladen Gogala wrote:
>
> Please, let us know what the outcome is. I am really curious now.
>
It doesn't make any difference. Sysadmin checked everything between the guest/host and the iSCSI box, they didn't see anything wrong. I now analyzed a long-running query (> 5 minutes) with a level 8 10046 trace. This is with async io enabled (disk_asynch_io=TRUE,filesystemio_options=SETALL):
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ Disk file operations I/O 3 0.00 0.00 db file sequential read 143264 0.78 242.64 latch: cache buffers lru chain 2 0.00 0.00 latch: object queue header operation 2 0.00 0.00 log file switch completion 3 0.06 0.15 db file scattered read 2333 0.07 4.93 asynch descriptor resize 1 0.00 0.00 log buffer space 3 0.13 0.25 direct path read temp 97 0.00 0.32 reliable message 67 0.00 0.03 latch: cache buffers chains 1 0.00 0.00
11 user SQL statements in session.
6 internal SQL statements in session.
17 SQL statements in session.
1 session in tracefile. 11 user SQL statements in trace file. 6 internal SQL statements in trace file. 17 SQL statements in trace file. 13 unique SQL statements in trace file. 5560145 lines in trace file. 716 elapsed seconds in trace file.
This is with async io disabled (disk_asynch_io=FALSE,filesystemio_options=NONE):
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ Disk file operations I/O 4 0.00 0.00 db file sequential read 166147 2.21 84.01 db file scattered read 2406 1.74 7.05 undo segment extension 2 0.01 0.01 log file switch completion 2 0.02 0.05 log buffer space 4 2.86 2.92 latch free 1 0.00 0.00 db file parallel read 2 0.15 0.19 direct path write temp 577 0.53 2.46 latch: shared pool 11 0.00 0.00 direct path read temp 577 0.01 0.54 latch: object queue header operation 1 0.00 0.00
11 user SQL statements in session.
6 internal SQL statements in session.
17 SQL statements in session.
1 session in tracefile. 11 user SQL statements in trace file. 6 internal SQL statements in trace file. 17 SQL statements in trace file. 13 unique SQL statements in trace file. 5583431 lines in trace file. 409 elapsed seconds in trace file.
So, you see, turning off async io drastically improves performance in my situation (409 versus 716 seconds). I'm going to leave it off for now, and maybe create a service request on MOS to see if they can help. I couldn't find a lot on OTN.
Matthias Hoys Received on Wed May 16 2012 - 03:32:51 CDT