Tom>I'll try to quantify it though. Do we have any existing test for these sorts of things? If not I'll just generate a bunch of data and pull it through - seems easy enough.
>Code affecting where incoming data goes would have to be registered with the statement object or similar before execution.
That is of no question. The question is "do you intend to call user-provided code right from org.postgresql.core.v3.QueryExecutorImpl#processResults, case 'D': // Data Transfer (ongoing Execute response)" ?