Re: Query kills machine.

Stef wrote:

> Christopher Kings-Lynne mentioned :
> => sort_mem = 4096
>
> Reducing sort_mem to 4096 seems to make it run in a reasonable time
> again. Any idea why? The database does a whole lot of huge sorts
> every day, so I thought upping this parameter would help.
>
> A couple of queries do seem to run slower now that I reduced
> the sort_mem.
> The shared buffers still makes a significant difference when I
increase it.
>

Well you have to take in account that sort_mem is not the total memory
allocated for sorting but per connection and in complex expressions
serveral times that too.

So if you sort a lot it can push your operating system off the cliff and
it might start reaping things that shouldn't be reaped and start swapping.

If that happens _everything_ on that box will get slow...

Shared buffers on the other hand is only allocated once.

Regards,
Magnus