Linux, Async io /direct IO

From: pier paolo Bruno <pbrunoster_at_gmail.com>
Date: Tue, 19 Feb 2013 14:11:35 +0100
Message-ID: <CA+dM1yP7i92sctw15Gj+cddREzKV2wDKJne2pa=uZx8_nSCQCw_at_mail.gmail.com>

We have an ovm infrastructure with Oracle 11.2.0.3 on Oracle Linux 5.8 64 bit. We used xen kernel (Oracle Linux Server-xen (2.6.18-308.el5xen)) with all database file on ext4 and we had filesystemio_options = ALL and disk_async_io= TRUE.
For a network performance problem oracle consultants told us to change kernel and we put Oracle Linux Server (2.6.32-300.10.1.el5uek). After a while the system was running with Oracle new kernel the instance become very very slow. It seems asyncronous IO become very slow . For verify if the problem is asyn Io I put filesystemio_options to none and disk_async_io to false.
Is there something i have to control for async IO and kernel sets ? I checked with support note 237299.1 .
regards
Pier Paolo

From awr :

                                        %Time Total Wait    wait    Waits
% bg
Event                             Waits -outs   Time (s)    (ms)     /txn

time

-------------------------- ------------ ----- ---------- ------- --------

---

db file async I/O submit 135 0 33 247 6.1 70.5
control file parallel writ 135 0 6 45 6.1 12.9
control file sequential re 221 0 4 16 10.0  7.6
log file parallel write 110 0 3 25 5.0  5.8

os thread startup                     8     0          0      29      0.4


  .5

db file sequential read               6     0          0      28      0.3


  .3

db file parallel write              135     0          0       0      6.1


  .0

latch free                           13     0          0       0      0.6

.0

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Received on Tue Feb 19 2013 - 14:11:35 CET