MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
The 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.
The cluster_locks table contains the
following columns:
node_id
ID of reporting node
block_instance
ID of reporting LDM instance
tableid
ID of table containing this row
fragmentid
ID of fragment containing locked row
rowid
ID of locked row
transid
Transaction ID
mode
Lock request mode
state
Lock state
detail
Whether this is first holding lock in row lock queue
op
Operation type
duration_millis
Milliseconds spent waiting or holding lock
lock_num
ID of lock object
waiting_for
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.
The 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.
The 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.
When the 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.
The op column shows the type of operation
requesting the lock. This is always one of the values
READ, INSERT,
UPDATE, DELETE,
SCAN, or REFRESH.
The 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 node_id,
block_instance, tableid,
fragmentid, and rowid.
The cluster_locks table was added in NDB
7.5.3.