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Memory Upgrade - kernel parms and swap

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Memory Upgrade - kernel parms and swap

We are running HP-UX 11i/Oracle 9i with 16Gb of RAM and 32Gb swap. We are experiencing performance issues with the Oracle Database and they are recommending we increase the amount of physical memory. We plan to double the RAM to 32Gb. dbc_min_pct is set to 3 and dbc_max_pct is set to 7. The Oracle SGA is set to 1.5Gb. swapmem_on is set to 0.
sar -b is reporting 100% read cache hits and 94% write cache hits.
Should I be looking at changing any of the HP-UX kernel parameters or swap? The DBA is initially planning to double the SGA to 3Gb. Any pointers will be gratefully received.
6 REPLIES
Oviwan
Honored Contributor

Re: Memory Upgrade - kernel parms and swap

Swap should be enough but you can set dbc_min_pct to 2 and dbc_max_pct to 5
Kenan Erdey
Honored Contributor

Re: Memory Upgrade - kernel parms and swap

Hi,

As your memory will be increased and these parameters take the percent, you can decrease parameters so that it will consume as much as space before you did the memory upgrade.

and as you'll fix memory problem, you can turn the swapmem_on to 1.

Kenan.
Computers have lots of memory but no imagination
Venkatesh BL
Honored Contributor

Re: Memory Upgrade - kernel parms and swap

- Looks like you are getting a good cache hit rate already! That means that your buffer cache size is quite adequate. So, you could update the dbc_max_pct to 5%.

- Set swapmem_on to 1. This will help in utilising the available space properly.

- After you change the SGA memory, you need observe the cache hit rates and update the dbc_max_pct, if required.

Re: Memory Upgrade - kernel parms and swap

Thanks for the replies. Please can you explain the benefit of switching swapmem_on?
Kenan Erdey
Honored Contributor

Re: Memory Upgrade - kernel parms and swap

when a process started it'll allocate as much swap as memory. if you give this memory from device swap, you'll consume disk space perhaps for never used swap. if you set swapmem_on, this space is allocated from memory, indeed not a real allocation just a mathematical calculation.
Computers have lots of memory but no imagination
Steven E. Protter
Exalted Contributor
Solution

Re: Memory Upgrade - kernel parms and swap

Shalom,

I would advise the following:

1) Figure out where you would locate additional swap space, but don't configure it immediately. Doubling memory should negate the paging that is going on. swapinfo -tam output would be nice to see.

2) Do not let the DBA change the SGA immediately. Wait for Oracle to do some self adjustment and monitor performance and judge the impact of memory increase prior to increasing the SGA. You may find your performance issues were due to swapping and immediately consuming additional memory for more SGA is not the best use of memory.

3) Check your system for memory leaks.

http://www.hpux.ws/?p=8

4) Monitor performance before and after the upgrade with a more comprehensive tool set.

http://www.hpux.ws/?p=6


swapmem_on=1 issue.
http://unix.derkeiler.com/Mailing-Lists/HP-UX-Admin/2004-01/0057.html

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=29191

swapmem obsolete????
http://docs.hp.com/en/B2355-60130/swapmem_on.5.html

Oracle performance tuning on HP-UX
http://docs.hp.com/cgi-bin/doc3k/BB316290001.14257/25

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Steven E Protter
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