On 12/12/05, Will Glynn <wglynn@freedomhealthcare.org> wrote:
> Mike Rylander wrote:
>
> >Right, I can definitely see that happening. Some backends are upwards
> >of 200M, some are just a few since they haven't been touched yet.
> >
> >
> >>Now, multiply that effect by N backends doing this at once, and you'll
> >>have a very skewed view of what's happening in your system.
> >>
> >
> >Absolutely ...
> >
> >>I'd trust the totals reported by free and dstat a lot more than summing
> >>per-process numbers from ps or top.
> >>
> >
> >And there's the part that's confusing me: the numbers for used memory
> >produced by free and dstat, after subtracting the buffers/cache
> >amounts, are /larger/ than those that ps and top report. (top says the
> >same thing as ps, on the whole.)
> >
>
> I'm seeing the same thing on one of our 8.1 servers. Summing RSS from
> `ps` or RES from `top` accounts for about 1 GB, but `free` says:
>
> total used free shared buffers cached
> Mem: 4060968 3870328 190640 0 14788 432048
> -/+ buffers/cache: 3423492 637476
> Swap: 2097144 175680 1921464
>
> That's 3.4 GB/170 MB in RAM/swap, up from 2.7 GB/0 last Thursday, 2.2
> GB/0 last Monday, or 1.9 GB after a reboot ten days ago. Stopping
> Postgres brings down the number, but not all the way -- it drops to
> about 2.7 GB, even though the next most memory-intensive process is
> `ntpd` at 5 MB. (Before Postgres starts, there's less than 30 MB of
> stuff running.) The only way I've found to get this box back to normal
> is to reboot it.
>
> >>>Now, I'm not blaming Pg for the apparent discrepancy in calculated vs.
> >>>reported-by-free memory usage, but I only noticed this after upgrading
> >>>to 8.1.
> >>>
> >>I don't know of any reason to think that 8.1 would act differently from
> >>older PG versions in this respect.
> >>
> >
> >Neither can I, which is why I don't blame it. ;) I'm just reporting
> >when/where I noticed the issue.
> >
> I can't offer any explanation for why this server is starting to swap --
> where'd the memory go? -- but I know it started after upgrading to
> PostgreSQL 8.1. I'm not saying it's something in the PostgreSQL code,
> but this server definitely didn't do this in the months under 7.4.
>
> Mike: is your system AMD64, by any chance? The above system is, as is
> another similar story I heard.
>
It sure is. Gentoo with kernel version 2.6.12, built for x86_64.
Looks like we have a contender for the common factor. :)
> --Will Glynn
> Freedom Healthcare
>
--
Mike Rylander
mrylander@gmail.com
GPLS -- PINES Development
Database Developer
http://open-ils.org
