RE: Odd swap & memory behavior on Solaris 9, Oracle 9iR2

Hi Matt,  

I ran into this a while ago, on boxes where the swap configuration was pretty skimpy. We had cases where we could not fully utilize available RAM due to swap shortages, and the fact that Solaris wants to "reserve" swap space equal to the amount of RAM being allocated.  

The solution was to find an "official" MetaLink note that recommends having swap 2x physical RAM, and using that and the "disk is cheap" argument to get the sysadmins to configure more swap. Once we did that, we never looked back, and there's been no problem.  

In reality, you can probably get away w/ 1.5x RAM, maybe less on boxes w/ really large amounts of RAM.  

Hope that helps,  

-Mark
 

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Mark J. Bobak
Senior Oracle Architect
ProQuest Information & Learning

For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled. --Richard P. Feynman, 1918-1988  

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Matthew Zito Sent: Monday, April 17, 2006 11:23 AM
To: oracle-l_at_freelists.org
Subject: Odd swap & memory behavior on Solaris 9, Oracle 9iR2

Howdy folks,

A friend of mine is seeing something odd on their Solaris 9/Oracle 9iR2 environment. They were having problems swapping constantly, and they gave me a call. They had their SGA + number of sessions * PGA sized significantly larger than their physical RAM, so I recommended they back everything down. However, the really odd behavior they see is that when they start up the Oracle instance, an amount of swap equivalent to their SGA is allocated, even when there's tons of free physical memory. Looking around metalink produced this little snippet from Note 151222.1:

"In Solaris 8, thanks to DISM support (Dynamic Intimate Shared Memory), it is
possible to avoid the above limitation and allocate the shared memory segment
such that only the active granules in the SGA are located in physical memory.
All unused granules will be stored in swap until needed.

NOTE: Swap space for the entire SGA_MAX_SIZE is required. See Note 230453.1
  for more details."

However, note 230453.1 doesn't exist anymore. I tested a similar config on a Solaris 8 box we have in our lab, and a similar behavior was not evidenced. Anyone have ideas where we should be looking?

Thanks,
Matt

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http://www.freelists.org/webpage/oracle-l Received on Mon Apr 17 2006 - 10:29:42 CDT