Re: Queries with large ResultSets

On Wed, 19 May 2004, Jack Orenstein wrote:

> If I'm reading the source code correctly, the PostgreSQL 7.3.4 JDBC
> driver creates a ResultSet by evaluating the entire query, and putting
> all the rows into a Vector. ResultSet.next() iterates over the
> Vector. Is that in fact what is happening?
>

Yes, in the 7.3 driver. The 7.4 driver (which works quite well against a
7.3 database) will use a cursor based fetch to retrieve a chunk of rows at
a time. There are a number of restrictions required to be able to use
this method (It only works with autocommit off and FORWARD_ONLY result
sets). To enable this use Statement.setFetchSize to indicate how many
rows at a time you want retrieved. Also there is a patch to the 7.5
driver to be able to retrieve subsets of the resultset for the scrollable
variety and hopefully I should get that in soon.

Kris Jurka