Horton

Re: Add SPLIT PARTITION/MERGE PARTITIONS commands

Alexander Korotkov <aekorotkov@gmail.com>

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From: Alexander Korotkov <aekorotkov@gmail.com>
To: Dmitry Koval <d.koval@postgrespro.ru>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2025-10-30T23:48:50Z
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. Adjust errcode in checkPartition()

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

  3. Implement ALTER TABLE ... SPLIT PARTITION ... command

  4. Implement ALTER TABLE ... MERGE PARTITIONS ... command

  5. Calculate agglevelsup correctly when Aggref contains a CTE.

  6. Use PqMsg_* macros in applyparallelworker.c.

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

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

  9. Use specific collation where needed in new test

  10. Expand virtual generated columns in the planner

  11. Virtual generated columns

  12. Define PG_LOGICAL_DIR for path pg_logical/ in data folder

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

  14. Avoid repeated table name lookups in createPartitionTable()

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

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

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

  18. Fix regression tests conflict in 3ca43dbbb6

  19. Add permission check for MERGE/SPLIT partition operations

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

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

  22. Add tab completion for partition MERGE/SPLIT operations

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

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

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

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

  27. Grammar fixes for split/merge partitions code

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

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

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

  31. Support identity columns in partitioned tables

  32. Fix indentation in twophase.c

  33. Fix corner-case planner failure for MERGE.

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

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

On Tue, Oct 28, 2025 at 1:12 AM Dmitry Koval <d.koval@postgrespro.ru> wrote:
> 1.
>  > The second CommandCounterIncrement() is needed to make the renamed
>  > relation visible within our transaction.  Why do we need the first
>  >one?  I see tests pass without it.
>
> It's strange. If I comment the first "CommandCounterIncrement();", in block
> -----------------------------------------------------------------------
> /*
>   * We must bump the command counter to make the split partition tuple
>   * visible for renaming.
>   */
> CommandCounterIncrement();
> /* Rename partition. */
> sprintf(tmpRelName, "split-%u-%X-tmp", RelationGetRelid(rel), ...);
> RenameRelationInternal(splitRelOid, tmpRelName, true, false);
> /*
>   * We must bump the command counter to make the split partition tuple
>   * visible after renaming.
>   */
> CommandCounterIncrement();
> -----------------------------------------------------------------------
> , I got the error "ERROR: tuple already updated by self" in the
> partition_split.sql test (Ubuntu). If I comment the second
> "CommandCounterIncrement();", I got the error "ERROR:  relation
> "sales_others" already exists" in the same test.

Sorry, actually it fails.  It appears that the first
CommandCounterIncrement() is needed to see the result of
detachPartitionTable().

> 2.
>  >The branch handling null value in the outer loop, uses null2 flag from
>  >the inner loop.  I think for the null value of the outer loop we still
>  >need to run inner loop to search for the matching null value.
>
> This code looks a little confusing, but it probably works correctly.
> This can be verified using two typical examples:
> -----------------------------------------------------------------------
> list1: (NULL, 1)
> list2: (2, NULL)
>
> (1) isnull1 = true, (2) "if (isnull1) lappend(NULL)"
> -----------------------------------------------------------------------
> list1: (1, NULL)
> list2: (NULL, 2)
>
> (1) isnull2 = true, (2) "if (isnull2) lappend(NULL)"
> -----------------------------------------------------------------------
> In both cases, we return from the function immediately after lappend.
> This works because we need to find exactly one repeating value.

How this function could handle this case?

list1: (NULL)
list2: whatever containing NULL

The outer loop will just quit after iterating the only element of
list1 without even iterating list2.

------
Regards,
Alexander Korotkov
Supabase