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Message-ID: <4BB49B0C.1050901@enterprisedb.com>
Date: Thu, 01 Apr 2010 16:09:32 +0300
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Organization: EnterpriseDB
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To: Fujii Masao <masao.fujii@gmail.com>
CC: Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	pgsql-docs@postgresql.org
Subject: Re: [HACKERS] Streaming replication document improvements
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Fujii Masao wrote:
> On Thu, Apr 1, 2010 at 11:00 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> On Wed, Mar 31, 2010 at 9:58 PM, Fujii Masao <masao.fujii@gmail.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