Re: OT - Blog entry on hugepages

  • From: "Rich Jesse" <rjoralist2@xxxxxxxxxxxxxxxxxxxxx>
  • To: "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 4 Apr 2012 16:10:08 -0500 (CDT)

Hey Kyle,

>   Does anyone have metrics to identify memory access problems on AIX other
> than paging and scanning stats that might be solved with largepages?
>   Recently an AIX customer  was seeing slow I/Os from an NFS filer but fast
> local I/O response times.  Of course the customer blamed the NFS filer, but
> the filer reported constant speeds during good periods as well as bad. I

Was CPU consistent between the tests?

Does the init.ora filesystemio_options='SETALL'?  I'm not sure how that
affects the NFS mount, but for JFS2 mounts, that will cause Oracle to
automagically use CIO (Ora10g and up) and also AIO, if enabled, IIRC. 
Oracle does this regardless of the mount options specified in
/etc/filesystems, again for JFS2.

I'm theorizing that if CIO's not used, there could be Oracle data files in
the filecache of the local storage, which could result in higher CPU while
still appearing as PIO to Oracle.  This would also depend on the VMO
filecache settings of minperm/maxperm/maxclient.  I watch the filecache
constantly in AIX's excellent nmon in the memory window, as well as a vmstat
monitoring script containing:

vmstat -v|grep -E 'numperm|file pages'

Hope this drivel helps!  I don't claim to be an expert in this, but have
been delving into this stuff now to help me determine how big I can make my
buffer cache w/o causing AIX (v5.3) paging.

GL!

Rich

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