Re: I want to send comments to the backend!

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Yes, I see that now. res is NULL and PQresultStatus() is returning
> > PGRES_NONFATAL_ERROR. What is strange is that "" and "\n" both return
> > an OK result, so I am trying to figure out why comments are different.
>
> The backend special-cases an input string that contains only whitespace
> (look in postgres.c). The special case doesn't apply here, though.
>
> >> Perhaps PGRES_EMPTY_QUERY would be more appropriate? Not sure where in
> >> the chain would be best to change the behavior, though.
>
> > Yes.
>
> Well, we could change the backend --- but that would be a nontrivial
> change, and to tell you the truth I think the special response for empty
> query is a wart on the protocol anyhow. In the long run I'd rather get
> rid of it.

Yes, I see that now:

if (strspn(parser_input->data, " \t\r\n") == parser_input->len)

> Or we could change PQexec to return a PGRES_EMPTY_QUERY result if it
> gets nothing back from the backend except ReadyForQuery. Question is,
> does that create the possibility of masking error conditions?
>
> Or we could just change PQresultStatus to return PGRES_EMPTY_QUERY for
> a null input. Attractive 'cause it's a one-line change, but I think it
> really does create the possibility of masking errors --- application
> programmer errors, mostly.

Could we change the backend to return NullCommand() if the query string
was empty, rather than checking for whitespace directly? I thought the
whitespace test was there only as a performance hack. In fact, the
comment in postgres.c says that:

* if there is nothing in the input buffer, don't
* bother trying to parse and execute anything; just
* send back a quick NullCommand response.

In pg_exec_query_string(), if nothing is processed, we can do the call
there. or course assuming destination is correct?

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