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Re: Row pattern recognition

Henson Choi <assam258@gmail.com>

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From: Henson Choi <assam258@gmail.com>
To: Tatsuo Ishii <ishii@postgresql.org>
Cc: vik@postgresfriends.org, er@xs4all.nl, jacob.champion@enterprisedb.com, david.g.johnston@gmail.com, peter@eisentraut.org, pgsql-hackers@postgresql.org
Date: 2026-02-25T07:57:01Z
Lists: pgsql-hackers 
Hi Tatsuo,

I recently purchased the ISO/IEC 19075-5:2021 standard document
through my company, and have started cross-referencing it against
the implementation.

> nocfbot-0005: Detect zero-consumption NFA cycles


The cycle detection itself is necessary, but I found a behavioral
difference from the standard (Section 7.2.8).

When a group body is nullable (e.g. A? in (A?){2,3}), the visited
bitmap blocks re-entry to the skipped variable, so the END element
never gets a chance to produce an exit state for count < min.
The standard/Perl allows empty iterations to count toward min.

I plan to fix this by adding a compile-time flag on END elements
that indicates the group body can iterate with empty matches.
When the flag is set, nfa_advance_end() will generate the exit
state even when count < min.

> nocfbot-0006: Allow A{0} quantifier
>

After reviewing the standard, I'd like to withdraw this patch.

Section 4.14.1 explicitly requires n > 0 for the {n} quantifier.
While A{0} works correctly as an epsilon transition with the cycle
detection in place, it violates the standard.

Since we aim for standard conformance, I think we should keep the
n >= 1 restriction for {n}.

I'll include this revert in the next patch set.

Best regards,
Choi

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Adjust cross-version upgrade tests for seg_out() fix

  2. Rationalize error comments in partition split/merge tests

  3. Add fast path for foreign key constraint checks

  4. Fix assorted pretty-trivial memory leaks in the backend.

  5. Add temporal FOREIGN KEY contraints

  6. Add trailing commas to enum definitions

  7. Remove obsolete executor cleanup code