Disable async IO at OS level

UNIX AIX
1

Hi ,

User claims that report refresh is taking longer time than usual time and asking us to disable async IO at OS level.

1 DB is running in this server
This is prod server
OS -- AIX

My question is would there be an impact to database and server if we disable async IO in OS?
is this the right way to fix the issue?

I found following note from Oracle document relevant to my change. Could you please check and comment on this?

Regards,
Maddy

2

I assume you're talking about Oracle DB. The version is unknown, but hopefully not elder than 10.2. Usual requirement from Oracle DBA is to switch on the async I/O on the server side. If you have Oracle 10.x or later you can enable Concurrent I/O by setting FILESYSTEMIO_OPTIONS to setall in Oracle configuration. Read e.g. this document - https://docs.oracle.com/cd/B28359\_01/server.111/b32009/appa_aix.htm and consult Oracle support if you in doubt. I personally wouldn't switch off async I/O on AIX.

3

Hi Agent,

Thanks for link and suggestions.

Oracle -- 11.2.0.2.0
currently filesystemio_options parameter is set to SETALL in the DB.

One of user's DBA has suggested to either to disable async IO or apply a patch as per attached document.
Could you please review it and share your thoughts on this?

Regards,
Maddy

4

Hi,

i would recomend to read the following tuning guides.
We used this guides to successfully optimize our database servers.

https://www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/WP100883

https://www-950.ibm.com/events/wwe/grp/grp017.nsf/vLookupPDFs/AIX\_Oracle\_Tuning\_2013/$file/AIX\_Oracle\_Tuning_2013.pdf

Use of Asynchronous I/O is strongly advised for Oracle workloads

Regards

P.S. Starting with AIX 6.1 and Oracle 11.2.0.2, Oracle DB automaticly intend to use CIO -> fastpath AIO!

5

According to your document it is likely your DB is affected by the problem (though i am not sure, i don't understand Oracle version counting not well enough for that). Note, though, that there seems to be a fix for the Oracle software available. IMHO it would be better to apply the necessary updates (patches, fixes or what that is called in Oracle) than to disable async I/O.

In general you need asynchronous I/O to speed up disk operations which is why Oracle (and other DBs) actually demand this option to be switched on. Switching it off may solve the problem at hand but i expect it to negatively impact performance overall. (Therefore it might be better to patch Oracle than to work around the problem at OS level.)

Further, even if you decide against patching Oracle you would better switch it off in Oracle. Asynchronous I/O is a service the OS offers. You (the application) can use it but it doesn't have to do so! Your provided paper goes on to suggest to set "DISK_ASYNCH_IO = false", which is an Oracle setting, not a OS setting. Therefore:

Yes - I'd prefer the apply-a-patch route as stated above, but if this is - for whatever reason - not possible the DBA will simply have to switch it off themselves.

I hope this helps.

bakunin