Re: Row pattern recognition

Hi,

Sorry, I forgot to attach the patch file in my previous email.

2026년 2월 7일 (토) PM 2:41, Henson Choi <assam258@gmail.com>님이 작성:

> Hi Tatsuo,
>
> +-- Filter function to normalize Storage memory values only (not NFA
>> statistics)
>> +-- Works for text, JSON, and XML formats
>>
>> What about add reasoning why only storage memory values are normalized
>> something like:
>>
>> -- NFA statistics should not change between platforms.
>
>
> Done. I've updated the comment to:
>
> -- Filter function to normalize Storage memory values only (not NFA
> statistics).
> -- NFA statistics should not change between platforms; if they do, it could
> -- indicate issues such as uninitialized memory access.
> -- Works for text, JSON, and XML formats.
>
> This round focused primarily on reviewing explain.c.  I believe we're
> getting close to the final version now.  Only the nodeWindowAgg.c
> code review remains on my side.
>
> For the next submission, would it be helpful if I resend all the
> incremental patches I've already sent since v42 together as separate
> per-patch files?
>
> I've also made some updates to the documentation (advanced.sgml and
> ref/select.sgml).  Could you take a look and let me know if there are
> any mistakes or if the changes look good to you?
>
> I've sent several incremental patches on top of v42, and the attached
> patch is the next one in that series.  Here are the changes:
>
> Bugs fixed:
>
> - Fix server crash in fillRPRPatternAlt() when an inner ALT is the
>   last element of an outer ALT's branch.  Both alternations tried to
>   set the 'next' pointer on the same endpoint element, triggering
>   Assert(pat->elements[endPos].next == RPR_ELEMIDX_INVALID).  Fix by
>   redirecting all elements in the branch that share the old target to
>   point to the outer ALT's afterAlt instead.
>   (Test: PATTERN (C (A | B) | D) -- inner ALT at end of outer branch)
>
> - Add BEGIN element to fillRPRPatternGroup().  Previously only END was
>   emitted for quantified groups, so groups with min=0 had no skip path
>   to bypass the group content.  Change to BEGIN/END pairs where
>   BEGIN.jump points past END (skip) and END.jump points to the first
>   child (loop-back).  Add nfa_advance_begin() to the NFA executor for
>   group entry and skip handling.
>   (Test: PATTERN (A ((B | C) (D | E))* F?) -- * group matching 0 times)
>
> - Fix deparse output producing wrong parenthesization for nested ALT
>   patterns.  The flat-loop approach could not correctly suppress double
>   parentheses for single-ALT groups or handle depth transitions around
>   alternation separators.  Refactor into mutual recursion:
>   deparse_rpr_elements, deparse_rpr_group, deparse_rpr_alt, and
>   deparse_rpr_var.
>
> - Fix deparse separator ordering for nested ALT: the ' | ' separator
>   was emitted before closing inner parentheses, producing output like
>   '(c (a | b | )d)' instead of '(c (a | b) | d)'.  Close parens to
>   match separator depth before emitting ' | '.
>
> - Fix missing ALT separator registration in deparse_rpr_alt() when an
>   ALT is the first element of an outer ALT's branch.  The code only
>   checked elem->next (always -1 for ALT markers) but not elem->jump,
>   which carries the outer branch's separator position.
>
> - Fix altEndPositions/altBranchStarts length mismatch caused by the
>   'if (*idx > branchStart)' guard that skipped empty branches.  Remove
>   the guard so both lists always have matching entries.
>
> - Fix RPRPatternNode.reluctant initialization in gram.y.  ALT, SEQ,
>   VAR, and GROUP primary productions used false (0) or left it
>   uninitialized (defaulting to 0 from palloc0), but 0 is a valid
>   ParseLoc meaning "location at offset 0".  Change all four creation
>   sites to use -1 (no location), matching the convention used by
>   ParseLoc throughout the parser.
>
> - Fix reluctant quantifier display in both explain.c and ruleutils.c.
>   A bare variable with reluctant ? (e.g. A?) was displayed as just 'a'
>   since there was no quantifier to attach ? to.  Now emit '{1}?' to
>   make the reluctant marker unambiguous.
>
> New optimization:
>
> - Add mergeConsecutiveAlts() to the SEQ optimization pipeline.  After
>   GROUP{1,1} unwrap, bare alternations like (A | B) become ALT nodes
>   in the SEQ.  This step detects consecutive identical ALT nodes and
>   wraps them in a GROUP with the appropriate quantifier, e.g.
>   (A | B) (A | B) (A | B) -> (A | B){3}.  Combined with the existing
>   mergeGroupPrefixSuffix, patterns like (A | B) (A | B)+ (A | B)
>   further reduce to (A | B){3,}.
>
> - Extend tryMultiplyQuantifiers() to fold nested GROUP quantifiers
>   (e.g. ((A B)+)* -> (A B)*) in addition to VAR quantifiers.
>
> Other changes:
>
> - Add RPR_VARID_BEGIN (252) to rpr.h for the new control element type.
>   Reduce RPR_VARID_MAX from 252 to 251 accordingly and update the
>   maximum-variables boundary tests.
>
> - Add RPR_DEPTH_NONE (255) as sentinel for top-level elements that
>   have no enclosing group.  Reduce RPR_DEPTH_MAX to 254 accordingly.
>
> - Add BEGIN handling to computeAbsorbabilityRecursive() so that
>   absorbability flags propagate correctly through group boundaries.
>
> - Extract show_rpr_nfa_stats() from show_windowagg_info() for NFA
>   statistics display.
>
> - Replace defensive NULL check in collectPatternVariables() with
>   Assert, since the caller guarantees a non-NULL pattern.
>
> - Pair each EXPLAIN test query in rpr_explain.sql with a
>   pg_get_viewdef() check via CREATE TEMP VIEW, verifying that both
>   the ruleutils (parse tree) and explain (bytecode) deparse paths
>   produce consistent PATTERN output.
>
> - Add comment to rpr_explain_filter() explaining why only Storage
>   memory values are normalized: NFA statistics should not change
>   between platforms, and variation would indicate issues such as
>   uninitialized memory access.
>
> Also add EXPLAIN test cases for nested ALT patterns, consecutive ALT
> merging, and ALT prefix/suffix merging.
>
> On a side note, I feel that the automata characteristics of RPR --
> state transitions, context management, absorbability, etc. -- tend to
> require a much larger volume of test cases than typical RDBMS/SQL
> features.  This seems unavoidable given the combinatorial nature of
> NFA execution.
>
> Best regards,
> Henson
>