Horton

Re: SQL:2011 application time

Matthias van de Meent <boekewurm+postgres@gmail.com>

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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
To: Paul Jungwirth <pj@illuminatedcomputing.com>
Cc: Peter Eisentraut <peter@eisentraut.org>, Robert Haas <robertmhaas@gmail.com>, jian he <jian.universality@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-06-12T15:48:59Z
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 Wed, 5 Jun 2024 at 22:57, Paul Jungwirth <pj@illuminatedcomputing.com> wrote:
>
> On Thu, May 9, 2024 at 5:44 PM Matthias van de Meent <boekewurm+postgres@gmail.com> wrote:
>  > Additionally, because I can't create my own non-constraint-backing
>  > unique GIST indexes, I can't pre-create my unique constraints
>  > CONCURRENTLY as one could do for the non-temporal case
>
> We talked about this a bit at pgconf.dev. I would like to implement it, since I agree it is an
> important workflow to support. Here are some thoughts about what would need to be done.
>
> First we could take a small step: allow non-temporal UNIQUE GiST indexes. This is possible according
> to [1], but in the past we had no way of knowing which strategy number an opclass was using for
> equality. With the stratnum support proc introduced by 6db4598fcb (reverted for v17), we could
> change amcanunique to true for the GiST AM handler. If the index's opclasses had that sproc and it
> gave non-zero for RTEqualStrategyNumber, we would have a reliable "definition of uniqueness". UNIQUE
> GiST indexes would raise an error if they detected a duplicate record.

Cool.

> But that is just regular non-temporal indexes. To avoid a long table lock you'd need a way to build
> the index that is not just unique, but also does exclusion based on &&.  We could borrow syntax from
> SQL:2011 and allow `CREATE INDEX idx ON t (id, valid_at WITHOUT OVERLAPS)`. But since CREATE INDEX
> is a lower-level concept than a constraint, it'd be better to do something more general. You can
> already give opclasses for each indexed column. How about allowing operators as well? For instance
> `CREATE UNIQUE INDEX idx ON t (id WITH =, valid_at WITH &&)`? Then the index would know to enforce
> those rules.

I think this looks fine. I'd like it even better if we could default
to the equality operator that's used by the type's default btree
opclass in this syntax; that'd make CREATE UNIQUE INDEX much less
awkward for e.g. hash indexes.

> This is the same data we store today in pg_constraint.conexclops. So that would get
> moved/copied to pg_index (probably moved).

I'd keep the pg_constraint.conexclops around: People are inevitably
going to want to keep the current exclusion constraints' handling of
duplicate empty ranges, which is different from expectations we see
for UNIQUE INDEX's handling.

> Then when you add the constraint, what is the syntax? Today when you say PRIMARY KEY/UNIQUE USING
> INDEX, you don't give the column names. So how do we know it's WITHOUT OVERLAPS? I guess if the
> underlying index has (foo WITH = [, bar WITH =], baz WITH &&) we just assume the user wants WITHOUT
> OVERLAPS, and otherwise they want a regular PK/UQ constraint?

Presumably you would know this based on the pg_index.indisunique flag?

> In addition this workflow only works if you can CREATE INDEX CONCURRENTLY. I'm not sure yet if we'll
> have problems there. I noticed that for REINDEX at least, there were plans in 2012 to support
> exclusion-constraint indexes,[2] but when the patch was committed in 2019 they had been dropped,
> with plans to add support eventually.[3] Today they are still not supported. Maybe whatever caused
> problems for REINDEX isn't an issue for just INDEX, but it would take more research to find out.

I don't quite see where exclusion constraints get into the picture?
Isn't this about unique indexes, not exclusion constraints? I
understand exclusion constraints are backed by indexes, but that
doesn't have to make it a unique index, right? I mean, currently, you
can write an exclusion constraint that makes sure that all rows with a
certain prefix have the same suffix columns (given a btree-esque index
type with <> -operator support), which seems exactly opposite of what
unique indexes should do.

Kind regards,

Matthias van de Meent
Neon (https://neon.tech)