Re: Pipeline mode and PQpipelineSync() - Mailing list pgsql-hackers

On 2021-Jun-23, Boris Kolpackov wrote:

> If, however, I execute it by checking for results before sending the
> next INSERT, I get the following call sequence:
> 
> PQsendQueryPrepared() # INSERT #1
> PQflush()
> PQsendQueryPrepared() # INSERT #2
> PQflush()
> ...
> PQsendQueryPrepared() # INSERT #~400
> PQflush()
> PQconsumeInput()      # At this point select() indicates we can read.
> PQgetResult()         # NULL (???)
> PQgetResult()         # INSERT #1
> PQgetResult()         # NULL
> PQgetResult()         # INSERT #2
> PQgetResult()         # NULL

IIUC the problem is that PQgetResult is indeed not prepared to deal with
a result the first time until after the queue has been "prepared", and
this happens on calling PQpipelineSync.  But I think the formulation in
the attached patch works too, and the resulting code is less surprising.

I wrote a test case that works as you describe, and indeed with the
original code it gets a NULL initially; that disappears with the
attached patch.  Can you give it a try?

Thanks

-- 
Álvaro Herrera       Valdivia, Chile
"Escucha y olvidarás; ve y recordarás; haz y entenderás" (Confucio)