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Re: Add SPLIT PARTITION/MERGE PARTITIONS commands

Alexander Korotkov <aekorotkov@gmail.com>

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From: Alexander Korotkov <aekorotkov@gmail.com>
To: Pavel Borisov <pashkin.elfe@gmail.com>
Cc: Dmitry Koval <d.koval@postgrespro.ru>, Justin Pryzby <pryzby@telsasoft.com>, pgsql-hackers@lists.postgresql.org
Date: 2026-06-30T19:38:00Z
Lists: pgsql-hackers 
Hi, Pavel!

On Tue, Jun 30, 2026 at 2:25 PM Pavel Borisov <pashkin.elfe@gmail.com> wrote:
> On Tue, 30 Jun 2026 at 15:07, Alexander Korotkov <aekorotkov@gmail.com> wrote:
> > On Fri, Jun 26, 2026 at 10:50 PM Alexander Korotkov
> > <aekorotkov@gmail.com> wrote:
> > > On Fri, Jun 26, 2026 at 6:20 PM Dmitry Koval <d.koval@postgrespro.ru> wrote:
> > > > If we exclude case with DEFAULT partition, MERGE PARTITIONS command was
> > > > intended to be used when an incorrect table partitioning was chosen.
> > > > For example, a table was initially partitioned by month, but later we
> > > > needed to change table partitioning by quarter. In this case, MERGE
> > > > PARTITIONS command should merge several adjacent partitions into one.
> > > > Current checks are made for this case.
> > > >
> > > >  >- If there's *no* default partition, then I think the check should be
> > > >  >relaxed; it's sufficient to verify that the bounds of the merged
> > > >  >partition do not overlap with any partition which is not being merged;
> > > >
> > > > It's probably possible to do this. But in this case, the command will
> > > > not exactly be "MERGE PARTITIONS" ("MERGE PARTITIONS & EXPAND"?).
> > >
> > > +1,
> > > We can implement a support for this for 20.  For 19, I propose to
> > > state the restriction more explicit in the docs.  See the attached
> > > patch.
> >
> > I'm going to push the docs patch if no objections.
> I looked at the doc patch. IMO "in order to be merged" is redundant.
> I'd propose following:
> "For range-partitioned tables, the ranges of merged partitions must be
> adjacent. This applies even if the partitioned table has no default
> partition."

I've included your suggestion.
Pushed and and backpatched to 19.

------
Regards,
Alexander Korotkov
Supabase

Commits

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

  1. doc: clarify MERGE PARTITIONS adjacency requirement

  2. Take into account default_tablespace during MERGE/SPLIT PARTITION(S)

  3. Create TOAST table for partitions made by MERGE/SPLIT PARTITION

  4. Adjust errcode in checkPartition()

  5. Fix usage of palloc() in MERGE/SPLIT PARTITION(s) code

  6. Implement ALTER TABLE ... SPLIT PARTITION ... command

  7. Implement ALTER TABLE ... MERGE PARTITIONS ... command

  8. Calculate agglevelsup correctly when Aggref contains a CTE.

  9. Use PqMsg_* macros in applyparallelworker.c.

  10. Restrict psql meta-commands in plain-text dumps.

  11. Ensure we have a snapshot when updating various system catalogs.

  12. Use specific collation where needed in new test

  13. Expand virtual generated columns in the planner

  14. Virtual generated columns

  15. Define PG_LOGICAL_DIR for path pg_logical/ in data folder

  16. Revert support for ALTER TABLE ... MERGE/SPLIT PARTITION(S) commands

  17. Avoid repeated table name lookups in createPartitionTable()

  18. Provide deterministic order for catalog queries in partition_split.sql

  19. Don't copy extended statistics during MERGE/SPLIT partition operations

  20. Fix the name collision detection in MERGE/SPLIT partition operations

  21. Fix regression tests conflict in 3ca43dbbb6

  22. Add permission check for MERGE/SPLIT partition operations

  23. Fix one more portability shortcoming in new test_pg_dump test.

  24. Inherit parent's AM for partition MERGE/SPLIT operations

  25. Add tab completion for partition MERGE/SPLIT operations

  26. Rename tables in tests of partition MERGE/SPLIT operations

  27. Make new partitions with parent's persistence during MERGE/SPLIT

  28. Document the way partition MERGE/SPLIT operations create new partitions

  29. Change the way ATExecMergePartitions() handles the name collision

  30. Grammar fixes for split/merge partitions code

  31. Checks for ALTER TABLE ... SPLIT/MERGE PARTITIONS ... commands

  32. Fix some grammer errors from error messages and codes comments

  33. Support TZ and OF format codes in to_timestamp().

  34. Support identity columns in partitioned tables

  35. Fix indentation in twophase.c

  36. Fix corner-case planner failure for MERGE.

  37. Doc: fix documentation example for bytea hex output format.

  38. Avoid repeated name lookups during table and index DDL.