126.96.36.199 The ndbinfo cluster_locks Table
cluster_locks table provides information about current lock requests holding and waiting for locks on
NDB tables in an NDB Cluster, and is intended as a companion table to
cluster_operations. Information obtain from the
cluster_locks table may be useful in investigating stalls and deadlocks.
cluster_locks table contains the following columns:
ID of reporting node
ID of reporting LDM instance
ID of table containing this row
ID of fragment containing locked row
ID of locked row
Lock request mode
Whether this is first holding lock in row lock queue
Milliseconds spent waiting or holding lock
ID of lock object
Waiting for lock with this ID
The table ID (
tableid column) is assigned internally, and is the same as that used in other
ndbinfo tables. It is also shown in the output of ndb_show_tables.
The transaction ID (
transid column) is the identifier generated by the NDB API for the transaction requesting or holding the current lock.
mode column shows the lock mode; this is always one of
S (indicating a shared lock) or
X (an exclusive lock). If a transaction holds an exclusive lock on a given row, all other locks on that row have the same transaction ID.
state column shows the lock state. Its value is always one of
H (holding) or
W (waiting). A waiting lock request waits for a lock held by a different transaction.
detail column contains a
* (asterisk character), this means that this lock is the first holding lock in the affected row's lock queue; otherwise, this column is empty. This information can be used to help identify the unique entries in a list of lock requests.
op column shows the type of operation requesting the lock. This is always one of the values
duration_millis column shows the number of milliseconds for which this lock request has been waiting or holding the lock. This is reset to 0 when a lock is granted for a waiting request.
The lock ID (
lockid column) is unique to this node and block instance.
The lock state is shown in the
lock_state column; if this is
W, the lock is waiting to be granted, and the
waiting_for column shows the lock ID of the lock object this request is waiting for. Otherwise, the
waiting_for column is empty.
waiting_for can refer only to locks on the same row, as identified by
cluster_locks table was added in NDB 7.5.3.