Re: PATCH: Batch/pipelining support for libpq

On Thu, Mar 30, 2017 at 12:08 PM, Michael Paquier <michael(dot)paquier(at)gmail(dot)com
> wrote:

> On Wed, Mar 29, 2017 at 12:40 PM, Vaishnavi Prabakaran
> <vaishnaviprabakaran(at)gmail(dot)com> wrote:
> > Michael Paquier wrote:
> >>Could you as well update src/tools/msvc/vcregress.pl, aka the routine
> >>modulescheck so as this new test is skipped. I am sure that nobody
> >>will scream if this test is not run on Windows, but the buildfarm will
> >>complain if the patch is let in its current state.
> >
> > Thanks for the finding. Hmm, modulescheck will not pick up test_libpq as
> > "subdircheck" will fail for this module(because it does not have
> > "sql"/"expected" folders in it) and hence it will be skipped.
> > But, Modified "Mkvcbuild.pm" to exclude "test_libpq" module, as this test
> > anyways will not be run in Windows and also because it uses linux
> specific
> > APIs(gettimeofday , timersub).
>
> src/port/gettimeofday.c extends things on Windows, and we could
> consider to just drop the timing portion for simplicity (except
> Windows I am not seeing any platform missing timersub). But that's
> just a point of detail. Or we could just drop those tests from the
> final patch, and re-implement them after having some psql-level
> subcommands. That would far better for portability.
>

Yes agree, having tests with psql meta commands will be more easy to
understand also. And, that is one of the reason I separated the patch into
two - code and test . So, yes, we can drop the test patch for now.

>
> > There are 2 cases tested here:
> >
> > 1. Example for the case - Using COPY command in batch mode will trigger
> > failure. (Specified in documentation)
> > Failure can be seen only when processing the copy command's results. That
> > is, after dispatching COPY command, server goes into COPY state , but the
> > client dispatched another query in batch mode.
> >
> > Below error messages belongs to this case :
> > Error status and message got from server due to COPY command failure are
> :
> > PGRES_FATAL_ERROR ERROR: unexpected message type 0x50 during COPY from
> > stdin
> > CONTEXT: COPY batch_demo, line 1
> >
> > message type 0x5a arrived from server while idle
>
> Such messages are really confusing to the user as they refer to the
> protocol going out of sync. I would think that something like "cannot
> process COPY results during a batch processing" would be cleaner.
> Isn't some more error handling necessary in GetCopyStart()?

Hmm, With batch mode, after sending COPY command to server(and server
started processing the query and goes into COPY state) , client does not
immediately read the result , but it keeps sending other queries to the
server. By this time, server already encountered the error
scenario(Receiving different message during COPY state) and sent error
messages. So, when client starts reading the result, already error messages
sent by server are present in socket. I think trying to handle during
result processing is more like masking the server's error message with new
error message and I think it is not appropriate.

>
>
> Attached the latest code and test patches.
>
> For me the test is still broken:
> ok 1 - testlibpqbatch disallowed_in_batch
> ok 2 - testlibpqbatch simple_batch
> ok 3 - testlibpqbatch multi_batch
> ok 4 - testlibpqbatch batch_abort
> ok 5 - testlibpqbatch timings
> not ok 6 - testlibpqbatch copyfailure
>
> Still broken here. I can see that this patch is having enough
> safeguards in PQbatchBegin() and PQsendQueryStart(), but this issue is
> really pointing out at something...
>
>
I will check this one with fresh setup again and I guess that this should
not block the code patch.

Thanks & Regards,
Vaishnavi
Fujitsu Australia.