Horton

Re: SQL:2011 application time

Paul A Jungwirth <pj@illuminatedcomputing.com>

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From: Paul A Jungwirth <pj@illuminatedcomputing.com>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: Corey Huinker <corey.huinker@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Jaime Casanova <jcasanov@systemguards.com.ec>
Date: 2022-01-06T05:44:54Z
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, Jan 5, 2022 at 8:07 AM Peter Eisentraut
<peter.eisentraut@enterprisedb.com> wrote:
>
> This patch set looks very interesting.

Thank you for the review!

I'll work on your feedback but in the meantime here are replies to
your questions:

> I'm confused about how to query tables based on application time
> periods.  Online, I see examples using AS OF, but in the SQL standard
> I only see this used for system time, which we are not doing here.

Correct, the standard only gives it for system time. I think
application time is intended to be more "in user space" so it's fine
to use regular operators in your WHERE condition against the time
columns, whereas system time is more of a managed thing---automatic,
read-only, possibly stored in a separate table. Having a special
syntax cue lets the RDBMS know it needs to involve the historical
records.

> validate_period(): Could use an explanatory comment.  There are a
> bunch of output arguments, and it's not clear what all of this is
> supposed to do, and what "validating" is in this context.

I'm not too happy with that function, but a previous reviewer asked me
to factor out what was shared between the CREATE TABLE and ALTER TABLE
cases. It does some sanity checks on the columns you've chosen, and
along the way it collects info about those columns that we'll need
later. But yeah all those out parameters are pretty ugly. I'll see if
I can come up with a stronger abstraction for it, and at the very
least I'll add some comments.

> MergeAttributes(): I would perhaps initially just prohibit inheritance
> situations that involve periods on either side.  (It should work for
> partitioning, IMO, but that should be easier to arrange.)

Okay. I'm glad to hear you think partitioning won't be too hard. It is
one of the last things, but to me it's a bit intimidating.

> I didn't follow why indexes would have periods, for example, the new
> period field in IndexStmt.  Is that explained anywhere?

When you create a primary key or a unique constraint (which are backed
by a unique index), you can give a period name to make it a temporal
constraint. We create the index first and then create the constraint
as a side-effect of that (e.g. index_create calls
index_constraint_create). The analysis phase generates an IndexStmt.
So I think this was mostly a way to pass the period info down to the
constraint. It probably doesn't actually need to be stored on pg_index
though. Maybe it does for index_concurrently_create_copy. I'll add
some comments, but if you think it's the wrong approach let me know.

> While reading this patch I kept wondering whether it would be possible
> to fold periods into pg_attribute, perhaps with negative attribute
> numbers.  Have you looked into something like that?  No doubt it's
> also complicated, but it might simplify some things, like the name
> conflict checking.

Hmm, I thought that sort of thing would be frowned upon. :-) But also
it seems like periods really do have a bunch of details they need
beyond what other attributes have (e.g. the two source attributes, the
matching range type, the period type (application-vs-system), maybe
some extra things for table inheritance.

Also are you sure we aren't already using negative attnums somewhere
already? I thought I saw something like that.

> Of course, the main problem in this patch is that for most uses it
> requires btree_gist.  I think we should consider moving that into
> core, or at least the support for types that are most relevant to this
> functionality, specifically the date/time types.  Aside from user
> convenience, this would also allow writing more realistic test cases.

I think this would be great too. How realistic do you think it is? I
figured since exclusion constraints are also pretty useless without
btree_gist, it wasn't asking too much to have people install the
extension, but still it'd be better if it were all built in.

> src/backend/access/brin/brin_minmax_multi.c
>
> These renaming changes seem unrelated (but still seem like a good
> idea).  Should they be progressed separately?

I can pull this out into a separate patch. I needed to do it because
when I added an `#include <rangetypes.h>` somewhere, these conflicted
with the range_{de,}serialize functions declared there.

> I don't understand why a temporal primary key is required for doing
> UPDATE FOR PORTION OF.  I don't see this in the standard.

You're right, it's not in the standard. I'm doing that because
creating the PK is when we add the triggers to implement UPDATE FOR
PORTION OF. I thought it was acceptable since we also require a
PK/unique constraint as the referent of a foreign key. But we could
avoid it if I went back to the executor-based FOR PORTION OF
implementation, since that doesn't depend on triggers. What do you
think?

Also: I noticed recently that you can't use FOR PORTION OF against an
updatable view. I'm working on a new patch set to fix that. But the
main reason is this PK check. So that's maybe another reason to go
back to the executor implementation.

> How to proceed.  I suppose we could focus on committing 0001 and 0002
> first.

That would be great! I don't think either is likely to conflict with
future system-time work.

> Is there anything else you think we can do as
> preparatory work to make the main patches more manageable?

I think it would be smart to have a rough plan for how this work will
be compatible with system-time support. Corey & I have talked about
that a lot, and In general they are orthogonal, but it would be nice
to have details written down somewhere.

Yours,
Paul