Re: CSStorm occurred again by postgreSQL8.2

Is there anything to do for 8.2 here?

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ITAGAKI Takahiro wrote:
> This is an additional information.
>
> I wrote:
> > If we want to resolve the probmen fundamentally, we might have to
> > improve SubTrans using a better buffer management algorithm or so.
>
> The above is maybe wrong. I checked each lwlock of pg_subtrans's buffers.
> All lwlocks are uniformly acquired and I could not see any differences
> among buffers. So the cause seems not to be a buffer management algorithm,
> but just a lack of SLRU buffer pages.
>
> NUM_SUBTRANS_BUFFERS is defined as 32 in HEAD. If we increase it,
> we can avoid the old transaction problem for a certain time.
> However, it doesn't help much on high-load -- for example, on a workload
> with 2000 tps, we will use up 1000 pg_subtrans pages in 15 minites.
> I suppose it is not enough for online and batch/maintenance mix.
>
> Also, the simple scanning way in SLRU will likely cause another performance
> issue when we highly increase the number of buffers. A sequential scanning
> is used in SLRU, so it will not work well against many buffers.
>
>
> I hope some cares in upper layer, snapshot, hitbits or something,
> being discussed in the recent thread.
>
> Regards,
> ---
> ITAGAKI Takahiro
> NTT Open Source Software Center
>
>
>
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Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

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