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

Mark Dilger <mark.dilger@enterprisedb.com>

From: Mark Dilger <mark.dilger@enterprisedb.com>

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

Cc: Andrew Dunstan <andrew@dunslane.net>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Joel Jacobson <joel@compiler.org>

Date: 2021-08-09T21:01:13Z

Lists: pgsql-hackers

Tom,

I can still trigger the old bug for which we thought we'd pushed a fix.  The test case below crashes on master (e12694523e7e4482a052236f12d3d8b58be9a22c), and also on the fixed version "Make regexp engine's backref-related compilation state more bulletproof." (cb76fbd7ec87e44b3c53165d68dc2747f7e26a9a).

Can you test if it crashes for you, too?  I'm not sure I see why this one fails when millions of others pass.

The backtrace is still complaining about regc_nfa.c:1265:

+select regexp_split_to_array('', '(?:((?:q+))){0}(\1){0,0}?*[^]');
+server closed the connection unexpectedly
+   This probably means the server terminated abnormally
+   before or while processing the request.
+connection to server was lost

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

Fix regexp misbehavior with capturing parens inside "{0}".
- 92620e82f6a1 12.9 landed
- 7e75fe390b68 9.6.24 landed
- 3ebd32e70c09 11.14 landed
- 244dd79923a1 14.0 landed
- 071146184a59 13.5 landed
- 062c4c791937 10.19 landed
- 65dc30ced64c 15.0 landed
Let regexp_replace() make use of REG_NOSUB when feasible.
- 18bac60ede44 15.0 landed
Fix bogus assertion in BootstrapModeMain().
- e12694523e7e 15.0 cited
Avoid determining regexp subexpression matches, when possible.
- 0e6aa8747d43 15.0 landed
Check the size in COPY_POINTER_FIELD
- c1132aae336c 15.0 cited
Make regexp engine's backref-related compilation state more bulletproof.
- cb76fbd7ec87 15.0 cited