On Sun, 19 Nov 2006, Mikko Tiihonen wrote:
I have not yet looked at this patch, but hopefully I can answer some of
the questions below.
> - is there any better way to obtain the result set field information
> in QueryExecutor? (org/postgresql/jdbc2/AbstractJdbc2Statement.java)
> * could the result set type information be obtained during the
> prepare so that they would be available even on the first execute?
Getting information on the prepare before execution is possible, but would
require an extra network roundtrip. There has been a lot of speculation
about the impact of such a change, but I don't believe anyone has
measured it. The other complication is that we often want/need to do a
Bind before Describe so we know what's coming back. Consider "SELECT ?",
calling setInt will make the describe come back with an int type. Without
that I think it may error with an unresolved type. So you might need to
do: Parse/Bind/Describe/Sync, process results of Describe,
Bind/Execute/Sync while all that happens right now in one network trip.
> - in which conditions should a prepared statement drop the cached
> fields? for example: can the result set fields ever change after
> the statement has been prepared?
PreparedStatement ps = conn.prepareStatement("SELECT ?");
ps.setInt(1,1);
ResultSet rs = ps.executeQuery();
ps.setLong(1,1);
rs = ps.executeQuery();
Here the returned type has changed. In this case the driver recognized
that the input types have changed and reparses the query behind the
scenes. I'm not sure where you are operating so you might be alright or
you might need extra work to handle this case.
> - How big fuzzyness should be supported by the driver. If a column is
> of type date and ResulSet.getTimestamp is called, should it work?
> * I currently support only getString on the time fields
> * I can make the getTime/getDate/getTimestamp interchangeable if
> requested. It would even be possible to use getLong for time
> fields which the text encoding never supported
Yes, getTimestamp on a date should work. Consult the JDBC spec for
details of all the conversions. In the JDBC 3 spec, appendix B table B-6
shows all the required conversions.
> - Must the different SQL time formats in java have different extreme
> small/large value handling than what postgresql internally uses?
Don't know what you mean.
> - if caching of Field information is allowed (at least in some
> circumstances), could the driver be optimised to only request a
> Describe on the first excution of a prepared statement (or once
> during prepare)?
>
Well it does depend on the Bind parameters, but yes doing it repeatedly is
often a waste of time.
Hopefully that helped and I'll be able to look at the patch this weekend.
Kris Jurka
