SHMMAX and Oracle SGA

[Heinz Gaertner]

Hi,

for the memory issue. As far as i know it is possible to lock the SGA. Normally only root can lock memory because normal users do not have the mlock privilige. You can set this for any user with the setprivgrp command (must be set with every reboot, so a startup script should do this). The other thing is to set the oracle database to allow locking of the SGA. The db-parameter is lock_sga. Sorry to say that this is only theoretical knowlegde, never tested this on a live system. Normally we do a memory sizing, so that you never will need to lock memory (because there is enough hardware).
For more information about shared memory you probably want to use the program shminfo. This little thing should be available at www.software.hp.com (sorry, don't have the exact link at the moment).

Hope this is helpful

Heinz

[Kimathi Njeru]

You have a whole lot of answers here that will point you in the right direction.

The correct Oracle parameter that you will want to use to lock your SGA in memory is 'pre_page_sga'.

This is a boolean that when set to TRUE, will load all SGA pages into memory. It might increase instance startup but you will see a slight improvement in performance with the amount of RAM that you have.

It is platform specific though!
Kim

[Tim Killinger]

Thanks for all the replys everyone..... I apreciate it... and I'm learning!

[Bill Hassell]

It's very important to differentiate between 64bit HP-UX (the operating system) and 64bit Oracle (an application program). There are far too many critical database apps running 32bit Oracle code on 64bit HP-UX which creates the memory limitations.

If your DBA is really running 64bit Oracle, then SGA can be several Gb in size and take advantage of in-memory sort areas, fast row insertions and bypass the HP-UX buffer cache with Oracle's built-in cache. Note that in order to bypass HP-UX's buffer cache, there are two steps:

- Make sure that all Oracle data and index lvols are separate mountpoints, and that rollback, redo and archive logs as well as Oracle executables and config files are not mixed into these data area mountpoints.

- Mount the data lvols are mounted with the options: rw,nosuid,delaylog,mincache=direct,convosync=direct,nodatainlog

NOTE: The options mincache and convosync are part of Advanced JFS, an optional product, but should be part of any Oracle installation. Once you have increased the Oracle SGA for a larger cache (perhaps 500 to 800 megs) and remounted the data/index lvols with the above options, the HP-UX buffer cache can be reduced to about 200 megs (for 8Gb RAM, that would be about 3 percent. Set (kernel parameters) dbc min to about 1 or 2 percent and dbc max to 3 or 4 percent.

Here is the link for the contributed program: shminfo:

ftp://contrib:9unsupp8@hprc.external.hp.com/sysadmin/programs/shminfo/

Note that IE has a big problem with ftp sites (this is not http://) so you'll need to go into Tools->Internet Options->Advanced and turn OFF the folder view for FTP sites.