Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Dilger <mark.dilger@enterprisedb.com>
Cc: Andrew Dunstan <andrew@dunslane.net>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Joel Jacobson <joel@compiler.org>
Date: 2021-08-10T15:15:22Z
Lists: pgsql-hackers 
I wrote:
> So AFAICS Perl is acting in the way I'm attributing to POSIX.
> But maybe we should actually read POSIX ...

I went to look at the POSIX spec, and was reminded that it lacks
backrefs altogether.  (POSIX specifies the "BRE" and "ERE" regex
flavors as described in our docs, but not "ARE".)  So there's no
help to be had there.  The fact that Perl doesn't throw an error
is probably the most useful precedent available.

			regards, tom lane

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.