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: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: David Rowley <dgrowleyml@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-07-06T00:54:46Z
Lists: pgsql-hackers 
... BTW, I thought of a consideration that we probably need some
answer for.  As far as I can see, the patch assigns NodeTag values
sequentially in the order it sees the struct declarations in the
input files; an order that doesn't have a lot to do with our past
practice.  The problem with that is that it's next door to impossible
to control the tag value assigned to any one struct.  During normal
development that's not a big deal, but what if we need to add a
node struct in a released branch?  As nodes.h observes already,

 * Note that inserting or deleting node types changes the numbers of other
 * node types later in the list.  This is no problem during development, since
 * the node numbers are never stored on disk.  But don't do it in a released
 * branch, because that would represent an ABI break for extensions.

We used to have the option of sticking new nodetags at the end of
the list in this situation, but we won't anymore.

It might be enough to invent a struct-level attribute allowing
manual assignment of node tags, ie

typedef struct MyNewNode pg_node_attr(nodetag=466)

where it'd be the programmer's responsibility to pick a nonconflicting
tag number.  We'd only ever use that in ABI-frozen branches, so
manual assignment of the tag value should be workable.

Anyway, this isn't something we have to have before committing,
but I think we're going to need it at some point.

			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