[SOLVED] Unique keys > 3072 bytes allowed in MariaDB versions

Unique keys > 3072 bytes allowed in MariaDB versions > 10.5

I discovered the normal 3072 byte key limitation in MariaDB 10.3 while running this statement:

ALTER TABLE table1 ADD UNIQUE INDEX idx_my_composite_uniqueai_usr_email_uniq (table2_uuid ASC, table3_uuid ASC, text_column ASC)

Which gave the expected error:

ERROR 1071 (42000) at line 31: Specified key was too long; max key length is 3072 bytes

DDL for table1:

CREATE TABLE table1
(
    uuid char(36) CHARACTER SET ascii NOT NULL,
    table2_fk_uuid char(36) CHARACTER SET ascii NOT NULL,
    table3_fk_uuid char(36) CHARACTER SET ascii NOT NULL,
    text_field varchar(1024) DEFAULT NULL,
    PRIMARY KEY (uuid),
    KEY fk_table2_fk_uuid (table2_fk_uuid),
    KEY fk_table3_fk_uuid (table3_fk_uuid),
    CONSTRAINT fk_table1_table2 FOREIGN KEY (table2_uuid) REFERENCES table2 (uuid) ON DELETE NO ACTION ON UPDATE NO ACTION,
    CONSTRAINT fk_table1_table3 FOREIGN KEY (table3_uuid) REFERENCES table3 (uuid) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3;

My understanding is that the total key length for this unique key is 1024 * 4 (because text_field column is CHARSET=utfmb3) + 36 * 2 = 4168 bytes.

I realize that shortening the text_field column width if possible is the best way to stay within the key length limitation. However, prior to understanding this I upgraded my MariaDB server to 10.5 and also to 10.6 and the ALTER TABLE command executes just fine and the key is created.

Has the key limitation been expanded in the later db version? I'm not see that it did in the MariaDB documentation. If not, what else am I missing?

Solution

The limitation was removed back in 10.4. Release notes mention it : "Unique indexes can be created on BLOB or TEXT fields (MDEV-371)"