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22.5.10.4 The ndbinfo cluster_locks Table
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 following table provides information about the columns in
the cluster_locks table. For each column, the
table shows the name, data type, and a brief description.
Additional information can be found in the notes following the
table.
Table 22.378 Columns of the cluster_locks table
| Column Name | Type | Description |
|---|---|---|
node_id |
integer | ID of reporting node |
block_instance |
integer | ID of reporting LDM instance |
tableid |
integer | ID of table containing this row |
fragmentid |
integer | ID of fragment containing locked row |
rowid |
integer | ID of locked row |
transid |
integer | Transaction ID |
mode |
string | Lock request mode |
state |
string | Lock state |
detail |
string | Whether this is first holding lock in row lock queue |
op |
string | Operation type |
duration_millis |
integer | Milliseconds spent waiting or holding lock |
lock_num |
integer | ID of lock object |
waiting_for |
integer | 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.
Document created the 26/06/2006, last modified the 26/10/2018
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