From: Josh Berkus <josh@agliodbs.com>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Greg Stark <gsstark@mit.edu>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Simplifying replication
Date: Wed, 27 Oct 2010 14:01:17 -0700
Message-ID: <4CC8931D.3040800@agliodbs.com> (raw)
In-Reply-To: <1288096049.1587.253.camel@ebony>
References: <201010220022.o9M0M8Q29438@momjian.us>
<4CC0DEDE.7060707@agliodbs.com>
<AANLkTin0RfGOvk20vLYYfCDzdf5Sf94aQ5V-xOBB+Kqx@mail.gmail.com>
<AANLkTik-L-68UpwgyBh5HtROzkEYQ297fiy7C-c6qRfX@mail.gmail.com>
<1288096049.1587.253.camel@ebony>
> You have to put the WAL files *somewhere* while you do the base backup.
> PostgreSQL can't itself work out where that is, nor can it work out
> ahead of time how big it will need to be, since it is up to you how you
> do your base backup. Setting a parameter to -1 doesn't make the problem
> go away, it just pretends and hopes it doesn't exist, but screws you
> badly if you do hit the wall.
Agreed. That's why I like the idea of having a
max_wal_size/min_wal_time instead of keep_wal_segments or
checkpoint_segments. It's relatively simple for a DBA to know how much
disk space s/he has for WAL, total, before locking up the system.
And to answer Robert's question, because now I understand what he was
getting at. The reason we want a min_wal_time is because we don't want
to keep a larger WAL around always. If more WAL were always better,
then we'd only need max_wal_size and we'd only recycle when we hit it.
Instead, we'd recycle whenever we passed max_wal_time. That's why I
said that I was assuming nothing of the sort.
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
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To: pgsql-hackers@postgresql.org
Cc: josh@agliodbs.com, simon@2ndQuadrant.com, robertmhaas@gmail.com, gsstark@mit.edu, bruce@momjian.us
Subject: Re: Simplifying replication
In-Reply-To: <4CC8931D.3040800@agliodbs.com>
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