Cleaning up large objects

Hi,

I have a problem with the cleanup of large objects.

My database consists of (mainly) one table that holds a date and an
associated large object id. The large object can be as big as 2 megabytes.

Every hour, I have a small method that removes all entries that are older
than a certain date:

private void cleanup(Connection dbConn, Date deleteTo) throws SQLException
{
try {
dbConn.setAutoCommit(false);
dbConn.setTransactionIsolation(Connection.TRANSACTION_READ_COMMITTED);
LargeObjectManager lobj = ((PGConnection)dbConn).getLargeObjectAPI();

PreparedStatement queryStmt = dbConn.prepareStatement(
"SELECT Values FROM MyTable WHERE From_Date < ?");
queryStmt.setTimestamp(0, new Timestamp(deleteTo.getTime()));
ResultSet rs = queryStmt.executeQuery();
try {
while (rs.next()) {
int oid = rs.getInt(1);
try {
lobj.delete(oid);
} catch (SQLException e) {e.printStackTrace();}
}
} finally {
rs.close();
}
PreparedStatement deleteStmt
= dbConn.prepareStatement("DELETE FROM MyTable WHERE From_Date < ?");
deleteStmt.setTimestamp(1, new Timestamp(deleteTo.getTime()));
deleteStmt.executeUpdate();
dbConn.commit();
} catch (SQLException e) {
dbConn.rollback();
throw e;
}

This program also seems to work, that means that I dont get any exceptions
from it.
Also, every night I run the "vacuum" command:

/usr/bin/vacuumdb -a -z

But: the data base keeps growing. The table MyTable seems to successfully
remove the entries, but the disk usage keeps high.

I am quit sure that the disk usage mainly comes from the LOBs since the disk
usage shrinks with exactly the speed I expect from the LOBs I put in.

What is wrong with my approach that it does not free the disk space?

Regards

Ole

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