data_locks table shows data
locks held and requested. Rows of this table have a
THREAD_ID column indicating the thread ID of
the session that owns the lock, and an
EVENT_ID column indicating the Performance
Schema event that caused the lock. Tuples of
values implicitly identify a parent event in other Performance
The parent wait event in the
The parent stage event in the
The parent statement event in the
The parent transaction event in the
To obtain details about the parent event, join the
columns with the columns of like name in the appropriate parent
event table. The relation is based on a nested set data model,
so the join has several clauses. Given parent and child tables
child, respectively, the join looks like
WHERE parent.THREAD_ID = child.THREAD_ID /* 1 */ AND parent.EVENT_ID < child.EVENT_ID /* 2 */ AND ( child.EVENT_ID <= parent.END_EVENT_ID /* 3a */ OR parent.END_EVENT_ID IS NULL /* 3b */ )
The conditions for the join are:
The parent and child events are in the same thread.
The child event begins after the parent event, so its
EVENT_IDvalue is greater than that of the parent.
The parent event has either completed or is still running.
To find lock information,
data_locks is the table containing
data_locks table shows only
existing locks, so these considerations apply regarding which
table contains the parent event:
For transactions, the only choice is
events_transactions_current. If a transaction is completed, it may be in the transaction history tables, but the locks are gone already.
For statements, it all depends on whether the statement that took a lock is a statement in a transaction that has already completed (use
events_statements_history) or the statement is still running (use
For waits, the logic is similar to that for statements; use
events_waits_current. However, so many waits are recorded that the wait that caused a lock is most likely gone from the history tables already.
Wait, stage, and statement events disappear quickly from the history. If a statement that executed a long time ago took a lock but is in a still-open transaction, it might not be possible to find the statement, but it is possible to find the transaction.
This is why the nested set data model works better for locating parent events. Following links in a parent/child relationship (data lock -> parent wait -> parent stage -> parent transaction) does not work well when intermediate nodes are already gone from the history tables.
The following scenario illustrates how to find the parent transaction of a statement in which a lock was taken:
 START TRANSACTION;  SELECT * FROM t1 WHERE pk = 1;  SELECT 'Hello, world';
SELECT ... FROM performance_schema.events_transactions_current AS parent INNER JOIN performance_schema.data_locks AS child WHERE parent.THREAD_ID = child.THREAD_ID AND parent.EVENT_ID < child.EVENT_ID AND ( child.EVENT_ID <= parent.END_EVENT_ID OR parent.END_EVENT_ID IS NULL );
The query for session B should show statement  as owning a
data lock on the record with
If session A executes more statements,  fades out of the history table.
The query should show the transaction that started in , regardless of how many statements, stages, or waits were executed.
To see more data, you can also use the
tables, except for transactions, assuming no other query runs in
the server (so that history is preserved).