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.


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