On 15/04/10 04:49, Dave Crooke wrote:
> Hi foilks
>
> I am using PG 8.3 from Java. I am considering a performance tweak which
> will involve holding about 150 java.sql.PreparedStatment objects open
> against a single PGSQL connection. Is this safe?
>
> I know that MySQL does not support prepared statements /per se/, and so
> their implementation of PreparedStatement is nothing more than some
> client-side convenience code that knows how to escape and format
> constants for you. Is this the case for PG, or does the PG JDBC driver
> do the real thing?
Pg supports real server-side prepared statements, as does the JDBC driver.
IIRC (and I can't say this with 100% certainty without checking the
sources or a good look at TFM) the PostgreSQL JDBC driver initially does
only a client-side prepare. However, if the PreparedStatement is re-used
more than a certain number of times (five by default?) it switches to
server-side prepared statements.
This has actually caused a bunch of performance complaints on the jdbc
list, because the query plan may change at that switch-over point, since
with a server-side prepared statement Pg no longer has a specific value
for each parameter and may pick a more generic plan.
Again only IIRC there's a configurable threshold for prepared statement
switch-over. I thought all this was in the PgJDBC documentation and/or
javadoc - if it's not, it needs to be.
--
Craig Ringer
