First of all, are you sure you need the whole table in memory? Maybe you should consider (if possible) selecting rows that you want to update/merge/etc. If you really have to have the whole table you could consider using a scrollable ResultSet. You can create it like this.
// make sure autocommit is off (postgres)
con.setAutoCommit(false);
Statement stmt = con.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE, //or ResultSet.TYPE_FORWARD_ONLY
ResultSet.CONCUR_READ_ONLY);
ResultSet srs = stmt.executeQuery("select * from ...");
It enables you to move to any row you want by using 'absolute' and 'relative' methods.
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