Re: Row pattern recognition

Hi Henson,

Thank you for the detailed design documentation. While learning the
document, just a quick comment and question.

> Hi hackers,
> 
> I've been working on an alternative implementation approach for Row
> Pattern Recognition (RPR) that addresses some limitations in the
> current regex-based patch.
> 
> Key differences from the existing approach:
> 
> 1. Streaming NFA instead of regex engine
>    - Process rows incrementally without accumulating encoded strings
>    - Avoids O(V^N) combinatorial explosion in multi-variable scenarios

Sounds good. As you already pointed out, current approach has a memory
space problem. If Streaming NFA could solve the issue, it would be
really good.

> 2. No 26-variable limit
>    - Variables identified by index, not alphabet encoding

Sounds good.

> 3. Proper Lexical Order support
>    - Respects PATTERN alternative order for ONE ROW PER MATCH

Here do you have "ONE ROW PER MATCH" option of RPR in your mind? In my
understanding it's in MATCH_RECOGNIZE clause, but not in RPR in Window
clause. (ALL ROWS PER MATCH is not applicable either in RPR in
Window clause).

> 4. GREEDY/RELUCTANT quantifier support
>    - Longest vs shortest match semantics

Sounds good.

> 5. Incremental MEASURES computation
>    - Aggregate values computed during matching, no rescan needed
> 
> The attached document describes the design in detail, including:
> - Data structures (Pattern, MatchState, MatchContext)
> - Execution flow and state transitions
> - Context absorption optimization for greedy patterns
> - AST optimization passes
> 
> This is still a work in progress. I'd appreciate any feedback on
> the approach before proceeding with PostgreSQL integration.

I understand you are still in the design phase and sorry for jumping
into an implementation question. but If you have an idea, please
advice:

How do you handle '{' and '}' in the PATTERN clause in the raw parser?
I am not a parser expert but it seems it's not easy to handle '{' and
'}' in gram.y.

Best regards,
--
Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp