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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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
