Re: Performance tuning on RedHat Enterprise Linux 3

On Tue, Dec 07, 2004 at 12:02:13PM +1100, Neil Conway wrote:
> On Mon, 2004-12-06 at 19:37 -0500, Paul Tillotson wrote:
> > I seem to remember hearing that the memory limit on certain operations,
> > such as sorts, is not "enforced" (may the hackers correct me if I am
> > wrong); rather, the planner estimates how much a sort might take by
> > looking at the statistics for a table.

> AFAIK this is not the case.

AFAIK this is indeed the case with hashed aggregation, which uses the
sort_mem (work_mem) parameter to control its operation, but for which it
is not a hard limit.

I concur however that multiple concurrent sorts may consume more memory
than the limit specified for one sort.  (Just last week I saw a server
running with sort_mem set to 800 MB ... no wonder the server went belly
up every day at 3.00am, exactly when a lot of reports were being
generated)

--
Alvaro Herrera (<alvherre[@]dcc.uchile.cl>)
"Acepta los honores y aplausos y perderás tu libertad"