Horton

Re: Another regexp performance improvement: skip useless paren-captures

Andrew Dunstan <andrew@dunslane.net>

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From: Andrew Dunstan <andrew@dunslane.net>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Joel Jacobson <joel@compiler.org>
Date: 2021-08-05T15:41:38Z
Lists: pgsql-hackers 
On 8/5/21 10:39 AM, Robert Haas wrote:
> On Thu, Aug 5, 2021 at 9:43 AM Andrew Dunstan <andrew@dunslane.net> wrote:
>> On 8/4/21 6:15 PM, Tom Lane wrote:
>>> Here's a little finger exercise that improves a case that's bothered me
>>> for awhile.  In a POSIX regexp, parentheses cause capturing by default;
>>> you have to write the very non-obvious "(?:...)" if you don't want the
>>> matching substring to be reported by the regexp engine.
>> It's not obscure to perl programmers :-)
> Well, I consider myself a pretty fair perl programmer, 


I also consider you one :-)


Perhaps I should have said "many perl programmers".


> and I know
> there's a way to do that, but I never do it, and I would have had to
> look up the exact syntax. So +1 from me for anything automatic that
> avoids paying the overhead in some cases.


Yeah, I'm not arguing against the idea. I also have to look it up,
mainly because there is such a huge amount of stuff that can follow
"(?", do "perldoc perlre" happens a lot when I'm doing that sort of work.


cheers


andrew


--
Andrew Dunstan
EDB: https://www.enterprisedb.com

Commits

  1. Fix regexp misbehavior with capturing parens inside "{0}".

  2. Let regexp_replace() make use of REG_NOSUB when feasible.

  3. Fix bogus assertion in BootstrapModeMain().

  4. Avoid determining regexp subexpression matches, when possible.

  5. Check the size in COPY_POINTER_FIELD

  6. Make regexp engine's backref-related compilation state more bulletproof.