Pseudoswap: when?

[Domenico Viggiani]

Hi all,
I'm in the process of upgrading a machine (with HP-UX 11.00) from 3GB to 6Gb of RAM.
Actually I have pseudoswap disabled and as much swap as physical memory.

Do I need only to enable pseudoswap or to add some (how much?) swap space?

Machine is an Oracle server.

[A. Clay Stephenson]

Anytime you have more memory than swapspace, pseudoswap should be enabled so that you can take advantage of all your RAM. If you have more swap than memory, then pseudoswap should be turned off.

[Stefan Farrelly]

Only if you want to load more processes into memory than you have RAM for should you use pseudo swap. Even if you have swap = RAM you should still have pseudo swap on because basically its a; SAFETY NET.
If RAM should ever get full instead of user processes dying due to lack of space errors, they will instead load and run (but start to slow the whole server down a bit until you free up some RAM or add some more!)

[S.K. Chan]

Typically if your swap space is less than your physical memmory you got to enable pseudo swap in order for more swap to be made available. The pseudo swap would be about 75% of the physical memory which the kernel recognizes.

[James R. Ferguson]

Hi:

One of the better (?) discussions we had on the merits of pseudoswap was this thread:

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x9e7487dc4d7dd5118ff00090279cd0f9,00.html

For more background, see the Technical Knowledge Base document "What is pseudo swap?", document #KBRC00001129.

Regards!

...JRF...

[Sandip Ghosh]

After upgradation of Memory watch for the utilisation of swap space (#swapinfo -mt)
If it appears that it is running out of swap you can always increase it online.

In my opinion, you should create another 3 GB of Swap space because during the server crash it should get the enough space to dump the contents of the swap.

Sandip

[julie huntington]

Pseduo swap was designed just for your type of situation.

Prior to pseudo swap , you had to have configured at least as much physical device swap as you had RAM. Now, if you enable pseudo swap by setting the "swapmem_on" kernel parameter set to 1, this restriction is lifted.

There's a good discussion about this in the white paper located at /usr/share/doc/mem_mgt.txt .