Swap usage

[LucianoCarvalho]

Hi Guys!
I have one question about swap. I have a system that is having almost 20% of swap area all the time. When I turn the database and all the otther applications off, this value begins to decrease, but will never be zero.
If I restart the system, and don't start any other application this value will be zero all the time.
Why does this vale not become zero?
I have 1 GB of memory and 2 GB of swap space.
Thanks

[A. Clay Stephenson]

First of all, you need more memory. 1GB is considered tiny these days for any sort of database use.

It's not really surprising that the value doesn't return to zero. Consider the case of a daemon, it's really doing absolutely nothing unless a request comes in; only then is it awakened. There is really no need to page this process back in until that moment.

You really need to use Glance (or vmstat) and examine the pageout rate. If the pageout rate is anything other than very small, your system is definitely under memory pressure.

[LucianoCarvalho]

Hi clay!
The pageout rate is about then. do you think this is a high number?

[Kent Ostby]

Luciano -- Where are you see the 20% ?

Is it in the reserved area or on the dev line ?

In swapinfo -t output, you will see several lines.

The "dev" lines show actual usage in the PCT USED column.

The "reserved" line shows space reserved for paging.

The "memory" line will appear if you are using psuedo swap.

Obviously the "total" line will be there as well on a swapinfo -t.

[LucianoCarvalho]

The 20% is been reported on dev line.

[twang]

If you are using oracle, check to see whether you pin the oracle sga in memory, recently I have dealed with an oracle database server(1.5GB RAM), the dba pins its sga in memory, results a very high page-out rate. In regard to this, I would suggest that it is possible to pin the oracle sga in memory if there is enough memory.