Date: Mon, 8 Jun 2020 14:05:26 -0500
From: Kenneth Marshall <ktm@rice.edu>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Magnus Hagander <magnus@hagander.net>,
	Michael Paquier <michael@paquier.xyz>,
	Amit Kapila <amit.kapila16@gmail.com>,
	David Fetter <david@fetter.org>,
	PostgreSQL Development <pgsql-hackers@postgresql.org>
Subject: Re: Bump default wal_level to logical
Message-ID: <20200608190526.GX22800@aart.rice.edu>
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On Mon, Jun 08, 2020 at 02:58:03PM -0400, Robert Haas wrote:
> On Mon, Jun 8, 2020 at 1:16 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> > I think it's reasonable to push our default limits for slots,
> > walsenders, max_bgworkers etc a lot higher than current value (say 10 ->
> > 100).  An unused slot wastes essentially no resources; an unused
> > walsender is just one PGPROC entry.  If we did that, and also allowed
> > wal_level to be changed on the fly, we wouldn't need to restart in order
> > to enable logical replication, so there would be little or no pressure
> > to change the wal_level default.
> 
> Wouldn't having a whole bunch of extra PGPROC entries have negative
> implications for the performance of GetSnapshotData() and other things
> that don't scale well at high connection counts?
> 

+1

I think just having the defaults raised enough to allow even a couple DB
replication slots would be advantageous and allow it to be used to
address spur of the moment needs for systems that need to stay up. It
does seem wasteful to by default support large numbers of slots and
seems to be contrary to the project stance on initial limits.

Regards,
Ken