EC
1517
MySQLERRORNotablePartitioningHIGH confidence

REORGANIZE PARTITION cannot change the number of HASH/KEY partitions

Production Risk

Low — the ALTER TABLE fails; use the correct command.

What this means

ER_REORG_HASH_ONLY_ON_SAME_NO (1517, SQLSTATE HY000) is raised when REORGANIZE PARTITION is used on HASH/KEY partitions to change their count, which is not supported.

Why it happens
  1. 1Attempting to use REORGANIZE PARTITION to split or merge HASH/KEY partitions
  2. 2REORGANIZE changes the structure but not the count for HASH/KEY; use ADD/COALESCE instead
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE t REORGANIZE PARTITION p0, p1 INTO (
  PARTITION pnew
);  -- Changing the count for HASH partition

expected output

ERROR 1517 (HY000): REORGANIZE PARTITION can only be used to reorganize partitions not to change their numbers

Fix

Use ADD PARTITION or COALESCE PARTITION to change HASH/KEY partition count

Use ADD PARTITION or COALESCE PARTITION to change HASH/KEY partition count
-- To increase HASH partition count:
ALTER TABLE t ADD PARTITION PARTITIONS 2;

-- To decrease:
ALTER TABLE t COALESCE PARTITION 2;

-- REORGANIZE works for RANGE/LIST to change boundaries:
ALTER TABLE range_t REORGANIZE PARTITION p0, p1 INTO (
  PARTITION pnew VALUES LESS THAN (200)
);

Why this works

ADD/COALESCE are the correct commands for changing HASH/KEY partition counts.

Sources
Official documentation ↗

MySQL 8.0 — 1517 ER_REORG_HASH_ONLY_ON_SAME_NO

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