Re: JDBC question for PG 8.3.9

On Wed, Apr 14, 2010 at 7:10 PM, Craig Ringer
<craig@postnewspapers.com.au> wrote:
> 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 is partially true. The driver uses an unnamed prepared statement
on the server.

> 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.

This is a limitation of the server, not the driver