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Re: Read only transactions - Commit or Rollback

From: Nörder-Tuitje, Marcus <noerder-tuitje(at)technology(dot)de>
To: "Grega Bremec" <gregab(at)p0f(dot)net>,"PostgreSQL Performance List" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Read only transactions - Commit or Rollback
Date: 2005-12-20 11:54:06
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Lists: pgsql-performance
Mmmm, good question.

MVCC blocks reading processes when data is modified. using autocommit implies that each modification statement is an atomic operation.

on a massive readonly table, where no data is altered, MVCC shouldn't have any effect (but this is only an assumption) basing on

using rowlevel locks with write access should make most of the mostly available to reading-only sessions, but this is an assumption only, too.

maybe the community knows a little more ;-)


-----Ursprüngliche Nachricht-----
Von: pgsql-performance-owner(at)postgresql(dot)org [mailto:pgsql-performance-owner(at)postgresql(dot)org]Im Auftrag von Grega Bremec
Gesendet: Dienstag, 20. Dezember 2005 12:41
An: PostgreSQL Performance List
Betreff: Re: [PERFORM] Read only transactions - Commit or Rollback

Hash: RIPEMD160

Nörder-Tuitje wrote:
|> We have a database containing PostGIS MAP data, it is accessed
|> mainly via JDBC. There are multiple simultaneous read-only
|> connections taken from the JBoss connection pooling, and there
|> usually are no active writers. We use connection.setReadOnly(true).
|> Now my question is what is best performance-wise, if it does make
|> any difference at all:
|> Having autocommit on or off? (I presume "off")
|> Using commit or rollback?
|> Committing / rolling back occasionally (e. G. when returning the
|> connection to the pool) or not at all (until the pool closes the
|> connection)?
| afaik, this should be completely neglectable.
| starting a transaction implies write access. if there is none, You do
| not need to think about transactions, because there are none.
| postgres needs to schedule the writing transactions with the reading
| ones, anyway.
| But I am not that performance profession anyway ;-)

Hello, Marcus, Nörder, list.

What about isolation? For several dependent calculations, MVCC doesn't
happen a bit with autocommit turned on, right?

- --
~    Grega Bremec
~    gregab at p0f dot net
Version: GnuPG v1.4.0 (GNU/Linux)


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Subject: Re: Read only transactions - Commit or Rollback
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