# Gap locks detection

The [Gap locks](https://dev.mysql.com/doc/refman/8.0/en/innodb-locking.html#innodb-gap-locks)
detection is based on a Facebook *MySQL* patch.

If a transactional storage engine does not support gap locks (for example
MyRocks) and a gap lock is being attempted while the transaction isolation
level is either `REPEATABLE READ` or `SERIALIZABLE`, the following SQL
error will be returned to the client and no actual gap lock will be taken
on the effected rows.

??? example "Error message"

    ```text
    ERROR HY000: Using Gap Lock without full unique key in multi-table or multi-statement transactions is not allowed. You need to either rewrite queries to use all unique key columns in WHERE equal conditions, or rewrite to single-table, single-statement transaction.
    ```