Re: nested transactions

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