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Re: nested transactions

From: Manfred Koizar <mkoi-pg(at)aon(dot)at>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>,PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: nested transactions
Date: 2002-11-29 11:23:26
Message-ID: 7qieuus4vec61laefvt5gi6mfl2rbklv8b@4ax.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, 28 Nov 2002 21:46:09 -0500, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
wrote:
>Manfred suggested a separate log file ("pg_subclog" or some such) but
>I really don't see any operational advantage to that.  You still end up
>with 4 bytes per transaction, you're just assuming that putting them
>in a different file makes it better.  I don't see how.

There are two points:

1) If your site/instance/application/whatever... does not use nested
transactions or does use them only occasionally, you don't have to pay
the additional I/O cost.

2) If we update a subtransaction's pg_clog bits as soon as the status
of the main transaction is known, pg_subtrans is only visited once per
subtransaction, while pg_clog has to be looked up once per tuple.

Things might look different however, if we wrap every command into a
subtransaction...

Servus
 Manfred

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