Re: Bug in libpq implentation and omission in documentation? - Mailing list pgsql-hackers

Ah ha. Yes, you're correct. It does mention here that an Int16 is used
to specify the number of parameter format codes, values etc. 

I suggest then that the documentation is updated to reflect this? Anf
again, perhaps the 'int' for nParams should be an int16_t or short?

Naturally I have already modified our code to batch or chunk rather
large numbers of parameters to fit within this restriction but I do
think it'd help others if the API interface reflected the same size data
types as the restricted back ends ;)

Thanks Dmitriy,

Jim

On Wed, 2012-08-08 at 13:27 +0400, Dmitriy Igrishin wrote:
> Hey Jim,
> 
> 2012/8/8 Jim Vanns <james.vanns@framestore.com>
>         Hello PG hackers. Yesterday I began diagnosing a peculiar bug
>         in some
>         production code that has been happily running for months. I
>         finally got
>         to the bottom of it despite the rather misleading error
>         message. Anyway,
>         within a section of code we are making a DELETE call to the
>         database via
>         the libpq call PQexecParams(). It failed with this message:
>         
>         'ERROR:  bind message has 32015 parameter formats but 1
>         parameters'
>         
>         This was just plain wrong. In fact, the # of parameters was
>         more like
>         80,000. The area of code is quite clear. Despite this being a
>         particularly large number of parameters (as you can imagine
>         this query
>         is built dynamically based on arbitrarily sized input) the
>         data type for
>         nParams for is a plain old 4-byte int. Upon further and deeper
>         inspection I find that this 4 byte int is truncated to two
>         bytes just
>         before going down the wire.
>         
>         There is no mention of any restriction in the 9.1.4
>         documentation:
>         
>         http://www.postgresql.org/docs/9.1/static/libpq-exec.html
>         
>         And the interface quite clearly accepts a 4 byte int however,
>         the PQsendQueryGuts()
>         function on line 1240 of src/interfaces/libpq/fq-exec.c just
>         blatantly truncates the
>         integer - it's calls pqPutInt() for nParams with a literal 2
>         rather than 4. It does this
>         several times, in fact.
>         
>         Unless I'm barking mad, surely this should either
>         
>         a) Be fixed and send 4 with nParams for pqPutInt() rather than
>         2
>         b) Documented (and the type changed) as only being a 2 byte
>         int
>            and therefore having a restriction on the number of
>         parameters
>            permitted in PQexecParams().
>         
>         Could someone either verify or correct me before I submit an
>         official bug report!?
>         
>         Regards,
>         
>         Jim Vanns
> AFAIK, this is a limitation of the frontend/backend protocol which
> allows
> you to bind no more than 2^16 parameters.
> See the description of the Bind (F) message here
> http://www.postgresql.org/docs/9.2/static/protocol-message-formats.html
> 
> 
> -- 
> // Dmitriy.
> 
> 

-- 
Jim Vanns
Systems Programmer
Framestore