Mmmm, good question.
MVCC blocks reading processes when data is modified. using autocommit implies that each modification statement is an
atomicoperation.
on a massive readonly table, where no data is altered, MVCC shouldn't have any effect (but this is only an assumption)
basingon
http://en.wikipedia.org/wiki/Mvcc
using rowlevel locks with write access should make most of the mostly available to reading-only sessions, but this is
anassumption only, too.
maybe the community knows a little more ;-)
regards,
marcus
-----Ursprüngliche Nachricht-----
Von: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.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
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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?
Cheers,
- --
~ Grega Bremec
~ gregab at p0f dot net
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