I think it's probably just reserving them. I can't think of anything else.
Also, when I run swap activity with sar I don't see any activity, which also
points to reserved swap space, not used swap space.
swap -s reports
total: 358336k bytes allocated + 181144k reserved = 539480k used, 2988840k
available
Kevin
----- Original Message -----
From: "Alan Stange" <stange@rentec.com>
To: "Kevin Schroeder" <kschroeder@mirageworks.com>
Cc: <pgsql-performance@postgresql.org>
Sent: Wednesday, January 19, 2005 11:04 AM
Subject: Re: [PERFORM] Swapping on Solaris
> Kevin Schroeder wrote:
>
>> I may be asking the question the wrong way, but when I start up
>> PostgreSQL swap is what gets used the most of. I've got 1282MB free RAM
>> right now and and 515MB swap in use. Granted, swap file usage probably
>> wouldn't be zero, but I would guess that it should be a lot lower so
>> something must be keeping PostgreSQL from using the free RAM that my
>> system is reporting. For example, one of my postgres processes is 201M
>> in size but on 72M is resident in RAM. That extra 130M is available in
>> RAM, according to top, but postgres isn't using it.
>
> The test you're doing doesn't measure what you think you're measuring.
>
> First, what else is running on the machine? Note that some shared
> memory allocations do reserve backing pages in swap, even though the pages
> aren't currently in use. Perhaps this is what you're measuring?
> "swap -s" has better numbers than top.
>
> You'd be better by trying a reboot then starting pgsql and seeing what
> memory is used.
>
> Just because you start a process and see the swap number increase doesn't
> mean that the new process is in swap. It means some anonymous pages had
> to be evicted to swap to make room for the new process or some pages had
> to be reserved in swap for future use. Typically a new process won't be
> paged out unless something else is causing enormous memory pressure...
>
> -- Alan
>
>
>
