| From: | Neil Conway <neilc(at)samurai(dot)com> |
|---|---|
| To: | Li YueXin <liyuexin(at)neusoft(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: A multi CUP performance problem |
| Date: | 2003-09-24 04:09:41 |
| Message-ID: | 1064376581.5822.5.camel@tokyo |
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| Lists: | pgsql-hackers |
On Tue, 2003-09-23 at 22:45, Li YueXin wrote:
> I found postgresql running on the multi CPU machine doesn't have
> better performance than single CPU machine. Can you explain the
> reason?
In addition to what Christopher Browne suggests, keep in mind that
PostgreSQL spawns a separate Unix process for each client connection.
Since each process can run on at most one CPU at any given time, if the
# of concurrent queries your application submits is < than the # of CPUs
in the machine, PostgreSQL won't take advantage of all your CPUs.
It would be possible to spread the execution of a single query over
multiple CPUs (say, have different nodes in the query tree execute on
different CPUs concurrently), but I highly doubt PostgreSQL will bother
doing that anytime soon.
-Neil
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