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Re: [HACKERS] Streaming replication document improvements

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, pgsql-docs(at)postgresql(dot)org
Subject: Re: [HACKERS] Streaming replication document improvements
Date: 2010-04-01 13:09:32
Message-ID: 4BB49B0C.1050901@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-docspgsql-hackers
Fujii Masao wrote:
> On Thu, Apr 1, 2010 at 11:00 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Wed, Mar 31, 2010 at 9:58 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>> You mean that we should change replication connection not to consume
>>> superuser_reserved_connections slots in 9.0?
>> Yes.

I think it's good that walsenders can use the superuser reserved slots,
that way a client that opens max_connections connections can't block out
standby servers from connecting.

> Preventing superuser connections from consuming superuser_reserved_connections
> slots seems strange for me. So I'm leaning toward just removing superuser
> privilege from replication connection again. Thought?

That would be good, but I fear it's a bigger change than we should be
doing at this point.

How about we adjust the backends math a bit:

Currently:

ReservedBackends = superuser_reserved_connections
MaxBackends = max_connections + autovacuum_max_workers + 1;

Proposal:

ReservedBackends = superuser_reserved_connections + max_wal_senders
MaxBackends = max_connections + autovacuum_max_workers + max_wal_senders + 1

So we implicitly reserve a slot and a superuser reserved slot for each
walsender. Walsenders use the slots reserved for superusers, but if you
set superuser_reserved_connections=3, there's still always at least
three slots available for superuser to log in with psql, even if the
maximum number of walsenders are connected.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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