Re: libpq sendQuery -- getResult not returning until all queries complete

On Wed, Dec 22, 2010 at 10:07 AM, Kelly Burkhart
<kelly(dot)burkhart(at)gmail(dot)com> wrote:
> On Tue, Dec 21, 2010 at 6:11 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
>>> On Tue, Dec 21, 2010 at 6:49 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>>> If you just unconditionally flush there, it will result in an extra
>>>> network message in the normal case where there's not another query
>>>> to do.  The current code is designed not to flush until it sends
>>>> ReadyForQuery.
>>
>>> yeah, I was looking at that.  I don't see an easy way to test if there
>>> is another query waiting to execute right there.  Maybe a
>>> documentation patch is in order :-).
>>
>> dest.c doesn't have the info available.  I think that to do this, we'd
>> need to move the responsibility for calling pq_flush out to postgres.c.
>> Not sure if it's worth it.
>
> So if I understand correctly, a flush will occur when all commands are
> completed and prior to completion, whenever PqSendBuffer is full.
> Analogous to stdio full vs. line buffering, this is full rather than
> result buffering.
>
> It seems to me that is not quite optimal and 'result buffering' would
> be better.  Did you come to the same conclusion but decide that it's
> not 'better enough' to justify polluting postgres.c with a special
> flush to satisfy this case?

The basic issue is that multiple queries per libpq call is more or
less a misfeature -- it's not worth refactoring the backend protocol
handling to peek ahead to know if it needs to flush on command
complete. Note that you can't use parametrized statements when using
this method, and use of parameterized statements should always be
encouraged.

Maybe there is another way to do what you are trying to do?

merlin