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From Knut Anders Hatlen <Knut.Hat...@Sun.COM>
Subject Re: [jira] Commented: (DERBY-822) Client driver: Pre-fetch data on executeQuery()
Date Sat, 11 Feb 2006 20:54:17 GMT
Bryan Pendleton <bpendleton@amberpoint.com> writes:

>> I am not convinced that the comment about LMTBLKPRC is correct, I
>> think it is also allowed for FIXROWPRC. Will look more into that.
>
> I think so, too, although there are a number of restrictions in the
> fixed row query protocol case. From page 126 of DRDA V.1:
>
>    For the fixed row query protocol, the qryrowset is a parameter on
>    the OPNQRY command that allows the requester to specify the return
>    of a rowset with the OPNQRYRM. This parameter applies only to
>    scrollable, non-sensitive dynamic, non-rowset cursors (QRYATTSCR
>    is TRUE, QRYATTSNS is not QRYSNSDYN, QRYATTSET is FALSE). For these
>    cursors, qryrowset specifies that a DRDA rowset is to be returned
>    with the OPNQRYRM (see Appendix B (on page 655) for more information
>    about DRDA rowsets). For all other cursors, the parameter is ignored
>    and no data is returned with the OPNQRYRM.
>
> Note that not only are there restrictions, but it also seems that
> the client has to request this rowset. We can't just send it
> automatically when the restrictions are met unless the client also
> sets qryrowset.

I think you are right, Bryan. The Query Data Transfer Protocol Rules
(DRDA Vol 1, p. 441) specify this in greater detail.

One thing that puzzles me is that the network server has no code for
returning QRYDTA in OPNQRYRM when the protocol is FIXROWPRC. The way I
read the spec, the server is required to return QRYDTA in FIXROWPRC
when qryrowset is non-zero (and there are no LOBs, and the cursor
doesn't support multi-row fetch). Does anyone know why it never sends
QRYDTA with OPNQRYRM? Could it be that FIXROWPRC is used only when
there are LOB columns? And does anybody know how Derby decides whether
FIXROWPRC or LMTBLKPRC should be used?

-- 
Knut Anders


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