Date: Mon, 8 Jun 2020 13:16:19 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: 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: <20200608171619.GA11063@alvherre.pgsql>
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On 2020-Jun-08, Tomas Vondra wrote:

> Not sure if it's sufficient, though, because switching to logical may
> require bumping up number of slots, walsenders, etc. At which point you
> actually need a restart. Not to mention that extensions using logical
> decoding (like pglogical) need to allocate shared memory etc. But for
> the built-in logical replication that is not an issue, ofc.

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.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services