Horton

Re: SQL:2011 application time

Paul A Jungwirth <pj@illuminatedcomputing.com>

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From: Paul Jungwirth <pj@illuminatedcomputing.com>
To: Peter Eisentraut <peter@eisentraut.org>, jian he <jian.universality@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-05-13T23:30:37Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Rename gist stratnum support function

  2. Remove support for temporal RESTRICT foreign keys

  3. Cache NO ACTION foreign keys separately from RESTRICT foreign keys

  4. Fix NO ACTION temporal foreign keys when the referenced endpoints change

  5. Improve whitespace in without_overlaps test

  6. Tests for logical replication with temporal keys

  7. Support for GiST in get_equal_strategy_number()

  8. Make the conditions in IsIndexUsableForReplicaIdentityFull() more explicit

  9. Replace get_equal_strategy_number_for_am() by get_equal_strategy_number()

  10. Improve internal logical replication error for missing equality strategy

  11. Simplify IsIndexUsableForReplicaIdentityFull()

  12. Fix ALTER TABLE / REPLICA IDENTITY for temporal tables

  13. doc: Update pg_constraint.conexclop docs for WITHOUT OVERLAPS

  14. doc: Add PERIOD to ALTER TABLE reference docs

  15. doc: Add WITHOUT OVERLAPS to ALTER TABLE reference docs

  16. Add temporal FOREIGN KEY contraints

  17. Add temporal PRIMARY KEY and UNIQUE constraints

  18. Add stratnum GiST support function

  19. Avoid crashing when a JIT-inlined backend function throws an error.

  20. Revert temporal primary keys and foreign keys

  21. Fix ON CONFLICT DO NOTHING/UPDATE for temporal indexes

  22. Add test for REPLICA IDENTITY with a temporal key

  23. Use half-open interval notation in without_overlaps tests

  24. Use daterange and YMD in without_overlaps tests instead of tsrange.

  25. Rename pg_constraint.conwithoutoverlaps to conperiod

  26. Fix comment on gist_stratnum_btree

  27. Add missing TAP test name

  28. Improve error handling of HMAC computations

  29. Rename functions to avoid future conflicts

On 5/13/24 03:11, Peter Eisentraut wrote:
> It looks like we missed some of these fundamental design questions early on, and it might be too 
> late now to fix them for PG17.
> 
> For example, the discussion on unique constraints misses that the question of null values in unique 
> constraints itself is controversial and that there is now a way to change the behavior.  So I 
> imagine there is also a selection of possible behaviors you might want for empty ranges.  
> Intuitively, I don't think empty ranges are sensible for temporal unique constraints.  But anyway, 
> it's a bit late now to be discussing this.
> 
> I'm also concerned that if ranges have this fundamental incompatibility with periods, then the plan 
> to eventually evolve this patch set to support standard periods will also have as-yet-unknown problems.
> 
> Some of these issues might be design flaws in the underlying mechanisms, like range types and 
> exclusion constraints.  Like, if you're supposed to use this for scheduling but you can use empty 
> ranges to bypass exclusion constraints, how is one supposed to use this?  Yes, a check constraint 
> using isempty() might be the right answer.  But I don't see this documented anywhere.
> 
> On the technical side, adding an implicit check constraint as part of a primary key constraint is 
> quite a difficult implementation task, as I think you are discovering.  I'm just reminded about how 
> the patch for catalogued not-null constraints struggled with linking these not-null constraints to 
> primary keys correctly.  This sounds a bit similar.
> 
> I'm afraid that these issues cannot be resolved in good time for this release, so we should revert 
> this patch set for now.

I think reverting is a good idea. I'm not really happy with the CHECK constraint solution either. 
I'd be happy to have some more time to rework this for v18.

A couple alternatives I'd like to explore:

1. Domain constraints instead of a CHECK constraint. I think this is probably worse, and I don't 
plan to spend much time on it, but I thought I'd mention it in case someone else thought otherwise.

2. A slightly different overlaps operator, say &&&, where 'empty' &&& 'empty' is true. But 'empty' 
with anything else could still be false (or not). That operator would prevent duplicates in an 
exclusion constraint. This also means we could support more types than just ranges & multiranges. I 
need to think about whether this combines badly with existing operators, but if not it has a lot of 
promise. If anything it might be *less* contradictory, because it fits better with 'empty' @> 
'empty', which we say is true.

Another thing a revert would give me some time to consider: even though it's not standard syntax, I 
wonder if we want to require syntax something like `PRIMARY KEY USING gist (id, valid_at WITHOUT 
OVERLAPS)`. Everywhere else we default to btree, so defaulting to gist feels a little weird. In 
theory we could even someday support WITHOUT OVERLAPS with btree, if we taught that AM to answer 
that question. (I admit there is probably not a lot of desire for that though.)

Yours,

-- 
Paul              ~{:-)
pj@illuminatedcomputing.com