Re: How much RAM is to much
From: Yong Huang <yong321_at_yahoo.com>
Date: Thu, 21 Apr 2011 12:37:11 -0700 (PDT)
Message-ID: <755874.6993.qm_at_web80606.mail.mud.yahoo.com>
> I'm wondering why there is the recommendation to use "forcedirectio" on
> the mount options when it seems, at least on solaris, that
> filesystemio_options=directio is sufficient for using direct I/O?
> - Kyle
Date: Thu, 21 Apr 2011 12:37:11 -0700 (PDT)
Message-ID: <755874.6993.qm_at_web80606.mail.mud.yahoo.com>
> I'm wondering why there is the recommendation to use "forcedirectio" on
> the mount options when it seems, at least on solaris, that
> filesystemio_options=directio is sufficient for using direct I/O?
> - Kyle
I tested on Linux using ext3 file system with Oracle 10.2.0.1. With filesystemio_options set, Oracle can open datafiles, log files, archive logs with O_DIRECT. But trace files, including alert.log, are opened without that flag. So if lots of big trace files are created, I think the file system page cache could be stressed.
By the way, Kyle, your two messages about your performance tests are very useful. A very minor point. forcedirectio (or equivalent) is more filesystem- than OS- specific. For instance, AIX's default or most popular filesystem JFS probably doesn't have this option. But if you use VxFS, you can specify convosync=direct.
Yong Huang
-- http://www.freelists.org/webpage/oracle-lReceived on Thu Apr 21 2011 - 14:37:11 CDT