Checks whether the lock named
str is free to use (that is, not locked).
1 if the lock is free (no one is using the lock),
0 if the lock is in use, and
NULL if an
error occurs (such as an incorrect argument, like an empty string or
str is case insensitive.
If the metadata_lock_info plugin is installed, the Information Schema metadata_lock_info table contains information about locks of this kind (as well as metadata locks).
Statements using the
IS_FREE_LOCK function are not safe for statement-based replication.
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