Currently, the Derby client contains a client-side implementation of
setQueryTimeout; using a TimerTask to invoke Statement.cancel() on the
client side. First of all, cancel() is not implemented, so this doesn't
work. Furthermore, we should use the server-side mechanism we now have
for statement timeouts.
For this, we need to transfer the timeout value from the client to the
server, preferable without a separate round-trip. I have some loose
thoughts on how to do this:
* If the client has set a timeout value for a statement, prepend the
(DRDA) EXCSQLSTT command with an EXCSQLSET command which contains the
timeout value; e.g., "SET STATEMENT TIMEOUT 10" (the actual wording is
not important for this general discussion).
* In DRDAConnThread.parseEXCSQLSETobjects() on the server side,
recognize the "SET STATEMENT TIMEOUT" text, parse the timeout value and
remember it for the coming EXCSQLSTT command. Do NOT invoke
executeUpdate() with the SET statement [see note below].
* In DRDAConnThread.parseEXCSQLSTT(), check if a timeout value has been
set; if so, use it (by setting the timeout value on the server-side
Statement object before calling execute/executeQuery).
Note: Instead of having the "SET STATEMENT TIMEOUT" syntax be understood
only by the Network Server, we could augment the Derby SQL grammar with
such a vendor-specific feature. In that case, I think the timeout value
should be considered session-wide; meaning, affecting all succeeding
statements on the same connection, with the same value, until modified.
This would support timeouts in SQL clients like ij. But this is not the
important part.
When going into details, we'll also need to consider the behaviour with
batched statements and prepared versus unprepared statements (different
DRDA commands are being sent from client to server), but at this early
stage I would just like to get some feedback on these general ideas.
--
Øyvind Bakksjø
Sun Microsystems, Web Services, Database Technology Group
Haakon VII gt. 7b, N-7485 Trondheim, Norway
Tel: x43419 / +47 73842119, Fax: +47 73842101
