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
$ LC_ALL=C /usr/bin/flex -Cfe -b /pgsql/source/REL8_4_STABLE/src/bin/psql/psqlscan.l
$ cat lex.backup
No backing up.
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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