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Home -> Community -> Mailing Lists -> Oracle-L -> RE: How much Max oracle memory (SGA)can be allocated on SUN SOLARIS if RAM =1.5gb
Seema
It is quite normal to have free memory to hover around this low. Read on if you are interested in knowing why.
From Solaris 2.6 onwards Virtual Memory Manager will use as much as memory available, to benefit file system random IO. If you have heavy random file system activity then the memory can be filled with these file pages. This might not be well suited for database environments.
Paging kicks-in when free memory falls below lotfree kernel parameter. Swapping and paging, can page out the process exec pages, heap and stack, even though the physical memory is filled with file pages (Whether SGA can be swapped/paged depends upon ISM-Intimate Shared Memory use, as the shared memory segments are locked if ISM is used ). This can create application performance issues, including database performance issues. Both background and server processes are susceptible to be paged out, if there is massive random IO.
Solaris 2.6+ introduced priority_paging to alleviate this. If priority paging is enabled, then the paging daemon pages the file pages when the free memory falls below a new parameter cachefree which is higher than lotfree. This paging will differentiate between file pages and anonymous pages and so the file pages will be paged out before process' pages are considered.
Solaris 2.8 introduces cyclical page cache, where the file and anonymous pages are handled differently. So, this issues should not exists in 2.8.
Point is, as long as you have priority_paging enabled in 2.6,
(In 2.7 it is enabled by default) you don't need to be concerned. I
would be concerned only if there is paging/swapping for anonymous pages.
Memstat can tell you what is being paged/swapped, if you are in 2.8. I
am not suggesting you to increase the SGA, by any means. That shoud be
decided by database/app behavior, not just by this..
HTH
Thanks
Riyaj "Re-yas" Shamsudeen
Certified Oracle DBA
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Seema Singh
Sent: Thursday, May 06, 2004 3:46 PM
To: oracle-l_at_freelists.org
Subject: How much Max oracle memory (SGA)can be allocated on SUN SOLARIS
if RAM =1.5gb
Hi
How much maximum SGA we can allocate if MEMORY on SUN Solaris is 1.5gb?
When sga alloacted to 220mb, top command show 46mb free.when I bumped
sga to
225mb it's still showing 46m is free.
thx-seema
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