Re: appendPQExpBufferVA vs appendStringInfoVA

On Sat, Nov 2, 2013 at 2:27 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > Tom commited some changes to appendStringInfoVA a few weeks ago which
> > allows it to return the required buffer size if the current buffer is not
> > big enough.
>
> > On looking at appendPQExpBufferVA I'm thinking it would be nice if it
> could
> > make use of the new pvsnprintf function to bring the same potential
> > performance improvement in to there too.
>
> Uh ... it does contain pretty much the same algorithm now. We can't
> simply use pvsnprintf there because exit-on-error is no good for
> libpq's purposes, so unless we want to rethink that, a certain
> amount of code duplication is unavoidable. But they both understand
> about C99 vsnprintf semantics now.
>
>
I only just noticed the changes you made to appendPQExpBufferVA().
I had wondered if making pvsnprintf return int instead of size_t and having
it return -1 if there are problems, then letting the caller deal with
those, but I'm starting to see why you did it the way you did it... There's
also quite a few subtle differences with things like max allocation size
that would have to be dealt with differently I guess.

I'm low on ideas on how to improve things much around here for now, but for
what it's worth, I did create a patch which changes unnecessary calls to
appendPQExpBuffer() into calls to appendPQExpBufferStr() similar to the
recent one for appendStringInfo and appendStringInfoString.

Regards

David Rowley

regards, tom lane
>