Originally posted by: chlawren

Hi all,

I have a question regarding swap as nobody can really give a straight answer ....

swap used to be and still may be on systems with small amount of memory 1.5 x physical memory ...

we have some oracle boxes with 24gb memory so setting the swap to 1.5 x seems a bit of overkill

A colleague has suggested because the memory is high we only need to set swap to .5 of physical memory - I would normally set swap the same size as physical memory.

does anyone have any other viable solutions?

Thanks in advance
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Originally posted by: unixgrl

Our rule of thumb is that we start with 8G of swap and add as needed. On the newer versions of AIX, there really should be no swapping at all. If you do find swap utilization is high, add another swap device that's the same size as the first, preferably on a different disk. Repeat as needed.

As I said, there should be little swapping - you should have enough memory to handle the app. In reality, there will be systems that are improperly sized or apps that don't use memory efficiently. Making swap be some percentage of total memory on every system will likely result
in wasted disk space on some, not enough on others.
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Originally posted by: Montecarlo

Swap space requirements really depend on application behaviour - not application requirements because some of them haven't been updated since memory was measured in kb.
Older rules for paging are based on early allocation model - in Aix 3 and maybe 4, memory allocation would result in equivalent paging space allocation because with the tiny physical memory available then it was highly likely that your system would swap. Nowadays with very large memory allocations, swapping is unlikely and early allocation of swap space does not occur.
A well behaved oracle installation with sensible memory allocation should not require significant swap space.
We run oracle databases on 24GB lpars with 8GB swap and never see paging space use. However, I've seen an oracle installation where dbas allocated more than available physical memory to oracle - so system swapped all the time.
How much memory is allocated in the oracle configuration?
Are there other applications on the system?
Regards, Simon
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Originally posted by: chlawren

ok that makes sense - thanks for the replies ....

I'll have a chat with the DBA's to identify the memory usage for oracle.

Thanks

Chris
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