On Thu, Mar 1, 2018 at 1:54 PM, Andres Freund <andres@anarazel.de> wrote:
> So this is hardcoded, without any sort of cache pressure logic? Doesn't
> that mean we'll often *severely* degrade performance if a backend is
> idle for a while?
Well, it is true that if we flush cache entries that haven't been used
in a long time, a backend that is idle for a long time might be a bit
slow when (and if) it eventually becomes non-idle, because it may have
to reload some of those flushed entries. On the other hand, a backend
that holds onto a large number of cache entries that it's not using
for tens of minutes at a time degrades the performance of the whole
system unless, of course, you're running on a machine that is under no
memory pressure at all. I don't understand why people keep acting as
if holding onto cache entries regardless of how infrequently they're
being used is an unalloyed good.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
