From: Stephen Frost <sfrost@snowman.net>
To: Thorsten Schöning <tschoening@am-soft.de>
Cc: pgsql-admin@lists.postgresql.org
Subject: Re: What's the dfifference between pg_start_backup+copy+pg_stop_backup+WAL vs. pg_start_backup+pg_stop_backup+copy+WAL?
Date: Fri, 23 Jul 2021 15:22:12 -0400
Message-ID: <20210723192212.GO20766@tamriel.snowman.net> (raw)
In-Reply-To: <1837868909.20210723211517@am-soft.de>
References: <1208702063.20210723115638@am-soft.de>
<399c734c5b9ffe10f68bcb79a69bea000d8d0c21.camel@cybertec.at>
<1751752722.20210723161202@am-soft.de>
<20210723152418.GK20766@tamriel.snowman.net>
<562203777.20210723194435@am-soft.de>
<6780C96C-3016-47C8-AD06-BF860283266C@elevated-dev.com>
<1837868909.20210723211517@am-soft.de>
Greetings,
* Thorsten Schöning (tschoening@am-soft.de) wrote:
> Guten Tag Scott Ribe,
> am Freitag, 23. Juli 2021 um 20:07 schrieben Sie:
>
> > Because it is in the file. WAL can re-do changes, it cannot undo them.
>
> But isn't visibility of rows associated to transaction numbers as
> well? I would have expected the transaction number for the row in B
> simply not being available, because it was never part of the WALs up
> to and including pg_stop_backup when not following the official
> ordering of commands. So I expected that row to simply not be visible
> at all and vacuumed at some point or whatever.
The information about what transactions have committed and what haven't
isn't just in the WAL- it's in the tuple header for frozen tuples, or
all visible tuples, and it's in the transaction log files otherwise, so
it would depend on when those are copied.
Thanks,
Stephen
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To: pgsql-admin@postgresql.org
Cc: sfrost@snowman.net, tschoening@am-soft.de, pgsql-admin@lists.postgresql.org
Subject: Re: What's the dfifference between pg_start_backup+copy+pg_stop_backup+WAL vs. pg_start_backup+pg_stop_backup+copy+WAL?
In-Reply-To: <20210723192212.GO20766@tamriel.snowman.net>
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