EC
3120
MariaDBERRORNotableDDLHIGH confidence

ALTER TABLE operation not supported for this reason

Production Risk

Medium — table copy can cause prolonged locks on large tables.

What this means

An ALTER TABLE statement requested an in-place or instant algorithm but the operation cannot be performed without a full table copy due to a specific constraint. The server reports the reason why the requested algorithm is not supported.

Why it happens
  1. 1The requested ALGORITHM=INPLACE or ALGORITHM=INSTANT is incompatible with the specific ALTER operation.
  2. 2Table properties (foreign keys, triggers, full-text indexes) prevent the optimised path.
How to reproduce
trigger — this will error
trigger — this will error
ALTER TABLE t1 ADD COLUMN x INT, ALGORITHM=INPLACE;

expected output

ERROR 3120 (HY000): ALGORITHM=INPLACE is not supported for this operation. Try ALGORITHM=COPY.

Fix 1

Allow COPY algorithm

Allow COPY algorithm
ALTER TABLE t1 ADD COLUMN x INT, ALGORITHM=COPY;

Why this works

COPY rebuilds the table and supports all ALTER operations.

Fix 2

Remove the ALGORITHM hint

Remove the ALGORITHM hint
ALTER TABLE t1 ADD COLUMN x INT;

Why this works

MySQL automatically selects the best supported algorithm.

What not to do

✕

Sources
Official documentation ↗

MySQL 8.0 — 3120 ER_ALTER_OPERATION_NOT_SUPPORTED_REASON2

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