Horton

Re: automatically generating node support functions

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>, David Rowley <dgrowleyml@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-07-14T21:42:10Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2021-06-08 19:45:58 +0200, Peter Eisentraut wrote:
>> On 08.06.21 15:40, David Rowley wrote:
>>> It's almost 2 years ago now, but I'm wondering if you saw what Andres
>>> proposed in [1]?

>> That project was technologically impressive, but it seemed to have
>> significant hurdles to overcome before it can be useful.  My proposal is
>> usable and useful today.  And it doesn't prevent anyone from working on a
>> more sophisticated solution.

> I think it's short-sighted to further and further go down the path of
> parsing "kind of C" without just using a proper C parser. But leaving
> that aside, a big part of the promise of the approach in that thread
> isn't actually tied to the specific way the type information is
> collected: The perl script could output something like the "node type
> metadata" I generated in that patchset, and then we don't need the large
> amount of generated code and can much more economically add additional
> operations handling node types.

I think the main reason that the previous patch went nowhere was general
resistance to making developers install something as complicated as
libclang --- that could be a big lift on non-mainstream platforms.
So IMO it's a feature not a bug that Peter's approach just uses a perl
script.  OTOH, the downstream aspects of your patch did seem appealing.
So I'd like to see a merger of the two approaches, using perl for the
data extraction and then something like what you'd done.  Maybe that's
the same thing you're saying.

I also see Peter's point that committing what he has here might be
a reasonable first step on that road.  Getting the data extraction
right is a big chunk of the job, and what we do with it afterward
could be improved later.

			regards, tom lane

Commits

  1. Fix MSVC build script's check for obsolete node support functions.

  2. Improve performance of ORDER BY / DISTINCT aggregates

  3. doc: Fix typos in protocol.sgml

  4. Tighten up parsing logic in gen_node_support.pl.

  5. Add defenses against unexpected changes in the NodeTag enum list.

  6. Add copy/equal support for XID lists

  7. Rationalize order of input files for gen_node_support.pl.

  8. Make assorted quality-of-life improvements in gen_node_support.pl.

  9. Doc: rearrange high-level commentary about node support coverage.

  10. Automatically generate node support functions

  11. Adjust node serialization tag of A_Expr for consistency

  12. Remove T_Join and T_Plan

  13. Reformat some more node comments

  14. Reformat some node comments

  15. Remove JsonPathSpec typedef

  16. Add missing enum tag in enum used in nodes

  17. Add Cardinality typedef

  18. Make node output prefix match node structure name

  19. Add WRITE_INDEX_ARRAY

  20. Add COPY_ARRAY_FIELD and COMPARE_ARRAY_FIELD

  21. Remove T_Expr

  22. Change NestPath node to contain JoinPath node

  23. Change SeqScan node to contain Scan node

  24. Check the size in COPY_POINTER_FIELD

  25. Remove T_MemoryContext

  26. Add missing enum tags in enums used in nodes

  27. Rename some node support functions for consistency

  28. Rename argument of _outValue()

  29. Rename NodeTag of ExprState