Re: Swapping on Solaris - Mailing list pgsql-performance

Well, easy it ain't and I believe it's good.  One final question:  When I
run sar -w I get no swap activity, but the process switch column registers
between 400 and 700 switches per second.  Would that be in the normal range
for a medium-use system?

Thanks
Kevin

----- Original Message -----
From: "Matt Clark" <matt@ymogen.net>
To: "Kevin Schroeder" <kschroeder@mirageworks.com>
Cc: <pgsql-performance@postgresql.org>
Sent: Wednesday, January 19, 2005 1:01 PM
Subject: Re: [PERFORM] Swapping on Solaris


> This page may be of use:
>
> http://www.serverworldmagazine.com/monthly/2003/02/solaris.shtml
>
> From personal experience, for god's sake don't think Solaris' VM/swap
> implementation is easy - it's damn good, but it ain't easy!
>
> Matt
>
> Kevin Schroeder wrote:
>
>> 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
>>>
>>>
>>>
>>
>>
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