Re: Server won't start with fallback setting by initdb.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Server won't start with fallback setting by initdb.
Date: 2018-03-06 22:58:36
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Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> writes:
> On 3/4/18 15:31, Tom Lane wrote:
>> Then, seeing that the factory defaults are ReservedBackends = 3 and
>> max_wal_senders = 10, something's got to give; there's no way that
>> max_connections = 10 can work with those. But what I would argue is that
>> of those three choices, the least defensible one is max_wal_senders = 10.
>> Where did that come from?

> Let's see. A typical installation might need:

> 1 for pg_receivewal for continuous backup
> 2 for pg_basebackup
> 2 for if pg_basebackup gets interrupted and it takes 2 hours to free the
> TCP/IP connections
> 1 for a standby connection
> 1 for a second standby connection, for making infrastructure changes

That's "typical"? It sounds like a major installation to me, one that
would certainly have had to fool with more settings than just
max_wal_senders. Two concurrent pg_basebackups running at all times
seems particularly dubious.

If we drop the assumption of 2 concurrent pg_basebackups, then your
math would lead to a value of 5, which I'd be OK with.

regards, tom lane

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