Check who holds a named lock. This function returns the connection identifier of the client holding the lock, or NULL if the lock is free.
IS_USED_LOCK(str)Checks whether the lock named str is in use (that is, locked). If so, it returns the connection identifier of the client that holds the lock. Otherwise, it returns NULL. str is case insensitive.
If the plugin is installed, the table contains information about locks of this kind (as well as ).
Statements using the IS_USED_LOCK function are .
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