Re: Bypassing shared_buffers

It could be cheaper, if the testing is done for many SELECT queries
sequentially - you need to flush dirty buffers just once pretty much.

-Vladimir Churyukin

On Wed, Jun 14, 2023 at 7:43 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> > There are two levels of cache. If you're on Linux you can ask it to
> > drop its caches by writing certain values to /proc/sys/vm/drop_caches.
> > For PostgreSQL's own buffer pool, it would be nice if someone would
> > extend the pg_prewarm extension to have a similar 'unwarm' operation,
> > for testing like that. But one thing you can do is just restart the
> > database cluster, or use pg_prewarm to fill its buffer pool up with
> > other stuff (and thus kick out the stuff you didn't want in there).
>
> But that'd also have to push out any dirty buffers. I'm skeptical
> that it'd be noticeably cheaper than stopping and restarting the
> server.
>
> regards, tom lane
>