Re: A couple of issues with psql variable substitution

On 08/25/2011 01:16 PM, Alvaro Herrera wrote:
> Excerpts from Tom Lane's message of jue ago 25 14:00:57 -0300 2011:
>> Robert Haas<robertmhaas(at)gmail(dot)com> writes:
>>> On Thu, Aug 25, 2011 at 12:47 PM, Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>>> 1. Somebody broke the no-backtracking property back in 9.0 while adding
>>>> quoted variable substitution. According to the flex manual, use of
>>>> backtracking creates a performance penalty. We once measured the
>>>> backend's lexer as being about a third faster with backtrack avoidance,
>>>> and presumably it's about the same for psql's. This is not hard to fix,
>>>> but should I consider it a bug fix and back-patch? We've not had
>>>> complaints about psql getting slower as of 9.0.
>>> That may well have been me.
>> [ checks "git blame" ] Well, you commmitted the patch anyway: d0cfc018.
>>
>>> How would I have known that I broke it?
>> Per the header comments in the backend lexer, you should run flex with
>> "-b" switch and verify that the resulting lex.backup file says "no
>> backing up". I've occasionally thought about automating that, but I'm
>> not sure if the output is entirely locale- and flex-version-independent.
> It is locale dependent, though of course for the automated check you
> could just run flex under LC_ALL=C.
>
> $ /usr/bin/flex -Cfe -b /pgsql/source/REL8_4_STABLE/src/bin/psql/psqlscan.l
> $ cat lex.backup
> Sin retroceso.
> $ LC_ALL=C /usr/bin/flex -Cfe -b /pgsql/source/REL8_4_STABLE/src/bin/psql/psqlscan.l
> $ cat lex.backup
> No backing up.
>

We could just add -b unconditionally to the flex flags and then count
the number of lines in lex.backup. If it's greater that 1 whine loudly,
or even fail, otherwise remove lex.backup. Would that avoid locale
dependencies?

cheers

andrew