Re: Row pattern recognition

>> One small concern is how to convert pattern variables to regex
>> expression which our regex enginer understands. Suppose,
>>
>> PATTERN UP+
>>
>> Currently I convert "UP+" to "U+" so that it can be fed to the regexp
>> engine. In order to do that, we need to know which part of the pattern
>> (UP+) is the pattern variable ("UP"). For "UP+" it's quite easy. But
>> for more complex regular expressions it would be not, unless PATTERN
>> grammer can be analyzed by our parser to know which part is the
>> pattern variable.
>
> Is the eventual plan to generate multiple alternatives, and run the
> regex against them one at a time?

Yes, that's my plan.

>>> I'm not familiar enough with this code yet to offer very concrete
>>> suggestions, sorry... But at some point in the future, we need to be
>>> able to skip forward and backward from arbitrary points, like
>>>
>>> DEFINE B AS B.price > PREV(FIRST(A.price), 3)
>>>
>>> so there won't be just one pair of "previous and next" tuples.
>>
>> Yes, I know.
>
> I apologize. I got overexplain-y.

No problem. Thank you for reminding me it.

>>> Maybe
>>> that can help clarify the design? It feels like it'll need to eventually
>>> be a "real" function that operates on the window state, even if it
>>> doesn't support all of the possible complexities in v1.
>>
>> Unfortunately an window function can not call other window functions.
>
> Can that restriction be lifted for the EXPR_KIND_RPR_DEFINE case?

I am not sure at this point. Current PostgreSQL executor creates
WindowStatePerFuncData for each window function and aggregate
appearing in OVER clause. This means PREV/NEXT and other row pattern
navigation operators cannot have their own WindowStatePerFuncData if
they do not appear in OVER clauses in a query even if PREV/NEXT
etc. are defined as window function.

> Or
> does it make sense to split the pattern navigation "functions" into
> their own new concept, and maybe borrow some of the window function
> infrastructure for it?

Maybe. Suppose a window function executes row pattern matching using
price > PREV(price). The window function already receives
WindowStatePerFuncData. If we can pass the WindowStatePerFuncData to
PREV, we could let PREV do the real work (getting previous tuple).
I have not tried this yet, though.

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