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Re: pgsql: Bootstrap WAL to begin at segment logid=0 logseg=1 (000000010000

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: pgsql: Bootstrap WAL to begin at segment logid=0 logseg=1 (000000010000
Date: 2010-11-03 14:31:55
Message-ID: 5824.1288794715@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> On 03.11.2010 11:34, Greg Stark wrote:
>> I'm actually not nearly so sanguine about this not affecting existing
>> installations. It means, for example, that anyone who has written
>> monitoring scripts that watch the wal position will see behaviour
>> they're not familiar with.

> You mean, they will see an unfamiliar wal position right after initdb? I 
> guess, but who runs monitoring scripts on a freshly initdb'd database 
> before doing anything on it?

The WAL position immediately after initdb is unspecified, and definitely
NOT 0/0, in any case.  From this perspective initdb will merely seem to
have emitted more WAL than it used to.

A possibly more realistic objection is that a slave freshly initdb'd
with 9.0.2 might have trouble syncing up with a master using 9.0.1,
if the master is so new it hasn't chewed a segment's worth of WAL yet.
Not sure if this is actually a problem.

			regards, tom lane

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