22.214.171.124 The ndbinfo server_locks Table
server_locks table is similar in structure to the
cluster_locks table, and provides a subset of the information found in the latter table, but which is specific to the SQL node (MySQL server) where it resides. (The
cluster_locks table provides information about all locks in the cluster.) More precisely,
server_locks contains information about locks requested by threads belonging to the current mysqld instance, and serves as a companion table to
server_operations. This may be useful for correlating locking patterns with specific MySQL user sessions, queries, or use cases.
server_locks table contains the following columns:
MySQL connection ID
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
mysql_connection_id column shows the MySQL connection or thread ID as shown by
block_instance refers to an instance of a kernel block. Together with the block name, this number can be used to look up a given instance in the
tableid is assigned to the table by
NDB; the same ID is used for this table in other
ndbinfo tables, as well as in the output of ndb_show_tables.
The transaction ID shown in the
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, which is always one of
S (shared lock) or
X (exclusive lock). If a transaction has 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 indicates whether this lock is the first holding lock in the affected row's lock queue, in which case it contains a
* (asterisk character); 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.
lock_state column's value is
W, this 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,
waiting_for is empty.
waiting_for can refer only to locks on the same row (as identified by
server_locks table was added in NDB 7.5.3.