An application is using the postgresql comunity jdbc driver v 9.4.1208 and I faced a problem because after analysing a java heap dump of the execution of big batch java procedure, I discover that the jdbc driver is keeping at the keep every row fetched. The jvm heap contained 1,2M rows and we have setup a defaultFetchSize of 5000 rows also I share you adiciontal detail, autocommit is false, ResultSet is TYPE_FORWARD_ONLY , ResultSet holdability is HOLD_CURSOR_OVER_COMMIT.
And the postgresql comunity jdbc driver 9.4 documentation said:
"
By default the driver collects all the results for the query at once. This can be inconvenient for large data sets so the JDBC driver provides a means of basing a ResultSet on a database cursor and only fetching a small number of rows.
A small number of rows are cached on the client side of the connection and when exhausted the next block of rows is retrieved by repositioning the cursor.
Note
Cursor based ResultSets cannot be used in all situations. There a number of restrictions which will make the driver silently fall back to fetching the whole ResultSet at once.
*The connection to the server must be using the V3 protocol. This is the default for (and is only supported by) server versions 7.4 and later.
*The Connection must not be in autocommit mode. The backend closes cursors at the end of transactions, so in autocommit mode the backend will have closed the cursor before anything can be fetched from it.
*The Statement must be created with a ResultSet type of ResultSet.TYPE_FORWARD_ONLY. This is the default, so no code will need to be rewritten to take advantage of this, but it also means that you cannot scroll backwards or otherwise jump around in the ResultSet.
*The query given must be a single statement, not multiple statements strung together with semicolons.
"
why the driver is storing so many rows because I think my connections satisfy all the conditions to ONLY store a limit number of rows.
Regards