Re: Keeping an Oracle 8.1.7 SGA in Physical Memory on Solaris 8

From: <jsc3_at_dontspamme.havoc.gtf.gatech.edu>
Date: Fri, 31 Aug 2001 13:05:40 +0000 (UTC)
Message-ID: <9mo234$9eu$1@news-int.gatech.edu>

In comp.sys.sun.admin Pete Finnigan <pete_at_peterfinnigan.demon.co.uk> alleged:

-> If you are looking to lock shared memory i take it you are having paging
-> issues. Check vmstat and search on google or whatever to read about
-> priority paging and what are real page in's and outs.

-> You should also look at the "priority paging" mechanism used in solaris.

-> add the parameter priority_paging=1 to your /etc/system This will stop
-> the kernel grabbing all the free kernel memory.

According to the "Solaris Tunable Parameters Reference Manual", you don't want to turn on priority paging if you are running Solaris 8:

"We recommend that all tuning of the VM system be removed from /etc/system.  Run with the default settings and determine if it is necessary to adjust  any of these parameters. Do not enable priority_paging or adjust cachefree.  These are no longer needed, although still present in the kernel.  Manipulating them will almost certainly result in performance degradation  when the page scanner runs."

This is also mentioned prominently in the Release Notes, in the "Upgrade Issues" section:

---

Priority Paging Is Not Needed With the New Solaris 8 Caching Architecture

The Solaris 8 operating environment introduces a new file system caching architecture, which subsumes the Solaris 7 Priority Paging functionality. You should not set the system variable priority_paging in the Solaris 8 operating environment, and you should remove the variable from the /etc/system file when systems are upgraded to the Solaris 8 operating environment.

The new caching architecture removes most of the pressure on the virtual memory system that resulted from file system activity. As a result, the new caching architecture changes the dynamics of the memory paging statistics, which makes observing system memory characteristics simpler. However, several of the statistics report significantly different values. You should consider these differences when analyzing memory behavior or setting performance monitoring thresholds. The most notable differences are:

      The number of page reclaims is higher, which you should
      consider normal operation during heavy file system activity.

      The amount of free memory is higher because the free memory
      count now includes a large component of the file system cache.

      Scan rates are almost zero unless there is a shortage of
      system-wide available memory. Scanning is no longer used to
      replace the free list during normal file system I/O.

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So, if you are running Solaris 2.6 or 7, by all means turn on priority paging, but don't use it with Solaris 8.

-- 
John Cronin
mailto: `echo NjsOc3_at_SgtPfA.orMg | sed 's/[NOSPAM]//g'`

Received on Fri Aug 31 2001 - 08:05:40 CDT