Re: Consecutive Query Executions with Increasing Execution Time

On Tue, Dec 17, 2019 at 8:08 AM Laurenz Albe <laurenz.albe@cybertec.at>
wrote:

> On Mon, 2019-12-16 at 15:50 -0500, Tom Lane wrote:
> > Peter Geoghegan <pg@bowt.ie> writes:
> > > Why do the first and the twentieth executions of the query have almost
> > > identical "buffers shared/read" numbers? That seems odd.
> >
> > It's repeat execution of the same query, so that doesn't seem odd to me.
>
> Really?  Shouldn't the blocks be in shared buffers after a couple
> of executions?
>

If it is doing a seq scan (I don't know if it is) they intentionally use a
small ring buffer to, so they evict their own recently used blocks, rather
than evicting other people's blocks.  So these blocks won't build up in
shared_buffers very rapidly just on the basis of repeated seq scans.

Cheers,

Jeff