Horton

Re: automatically generating node support functions

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-03-24T21:57:29Z
Lists: pgsql-hackers 
On Fri, 18 Feb 2022 at 19:52, Peter Eisentraut
<peter.eisentraut@enterprisedb.com> wrote:
> [ v5-0001-Automatically-generate-node-support-functions.patch ]

I've been looking over the patch and wondering the best way to move
this forward.

But first a couple of things I noted down from reading the patch:

1. You're written:

 * Unknown attributes are ignored.  Some additional attributes are used for
 * special "hack" cases.

I think these really should all be documented.  If someone needs to
use one of these hacks then they're going to need to trawl through
Perl code to see if you've implemented something that matches the
requirements.  I'd personally rather not have to look at the Perl code
to find out which attributes I need to use for my new field. I'd bet
I'm not the only one.

2. Some of these comment lines have become pretty long after having
added the attribute macro.

e.g.

PlannerInfo *subroot pg_node_attr(readwrite_ignore); /* modified
"root" for planning the subquery;
   not printed, too large, not interesting enough */

I wonder if you'd be better to add a blank line above, then put the
comment on its own line, i.e:

 /* modified "root" for planning the subquery; not printed, too large,
not interesting enough */
PlannerInfo *subroot pg_node_attr(readwrite_ignore);

3. My biggest concern with this patch is it introducing some change in
behaviour with node copy/equal/read/write.  I spent some time in my
diff tool comparing the files the Perl script built to the existing
code.  Unfortunately, that job is pretty hard due to various order
changes in the outputted functions.  I wonder if it's worth making a
pass in master and changing the function order to match what the
script outputs so that a proper comparison can be done just before
committing the patch.   The problem I see is that master is currently
a very fast-moving target and a detailed comparison would be much
easier to do if the functions were in the same order. I'd be a bit
worried that someone might commit something that requires some special
behaviour and that commit goes in sometime between when you've done a
detailed and when you commit the full patch.

Although, perhaps you've just been copying and pasting code into the
correct order before comparing, which might be good enough if it's
simple enough to do.

I've not really done any detailed review of the Perl code. I'm not the
best person for that, but I do feel like the important part is making
sure the outputted files logically match the existing files.

Also, I'm quite keen to see this work make it into v15.  Do you think
you'll get time to do that? Thanks for working on it.

David

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