Re: dependency between numbers keywords and parser speed

2011/3/15 Robert Haas <robertmhaas@gmail.com>:
> On Tue, Mar 15, 2011 at 2:19 AM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>> 2011/3/15 Robert Haas <robertmhaas@gmail.com>:
>>> On Mon, Mar 14, 2011 at 4:34 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>> Pavel Stehule <pavel.stehule@gmail.com> writes:
>>>>> there was a discussion about impact of number of keyword for parser
>>>>> speed. I did some synthetic tests and I didn't see any slowness on
>>>>> pgbench when I increased a number of keywords.
>>>>
>>>> I don't see any particular reason to suppose that pgbench would be a
>>>> good framework for stressing parsing speed.  The queries it issues
>>>> are of trivial length.
>>>
>>> I found that it was actually a fairly measurable component of the
>>> select-only test when running with shared_buffers cranked up to a
>>> reasonable value.  But it'd probably be a lot easier to measure on a
>>> benchmark specifically targeted at the parser.
>>>
>>
>> When I tested it - all data was in memory, there was a minimal (near
>> zero IO) and I run read only test.
>>
>> It doesn't mean, so parser is gratis, but my numbers doesn't show any
>> potential problem with 60 new keywords.
>
> That's an interesting result, although it would be more interesting if
> you posted the patch and benchmark methodology.  It's important for us
> not to overestimate the cost of adding keywords, and I don't object to
> adding them where it adds meaningful clarity that is not otherwise
> available or where it is necessary to comply with the SQL spec.  But I
> do think it is worth being disciplined about.  We should think about
> wording commands in a way that won't require new keywords; if there's
> not a reasonable way to do it, then we add a keyword.  Our preference
> should be not to add keywords where that's reasonably possible.
>
> It is particularly important for us to avoid keywords that are
> partially or fully reserved.  In that case, the issue is not parser
> overhead but the fact that it breaks compatibility with previous
> releases.  pg_dump files can't be loaded, PL/pgsql procedures break,
> and so on.  I have been here and it isn't fun.
>

I agree and I understand well a problems with keywords. Just I would
to know a real limits of bison and I can say so 60 keywords are not a
problem.

Real test of parser's speed should be done on short and quick queries.
It can be unexpected so parser should be a bottle neck on long OLAP
queries.

Patch is added

Pavel

p.s. I am sure so this test depends on platform.

> --
> Robert Haas
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