MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4
The data exposed by the transaction and locking tables
(INFORMATION_SCHEMA
INNODB_TRX table, Performance
Schema data_locks and
data_lock_waits tables) represents
a glimpse into fast-changing data. This is not like user tables,
where the data changes only when application-initiated updates
occur. The underlying data is internal system-managed data, and
can change very quickly:
Data might not be consistent between the
INNODB_TRX,
data_locks, and
data_lock_waits tables.
The data_locks and
data_lock_waits tables expose
live data from the InnoDB storage engine,
to provide lock information about the transactions in the
INNODB_TRX table. Data
retrieved from the lock tables exists when the
SELECT is executed, but might
be gone or changed by the time the query result is consumed
by the client.
Joining data_locks with
data_lock_waits can show rows
in data_lock_waits that
identify a parent row in
data_locks that no longer
exists or does not exist yet.
Data in the transaction and locking tables might not be
consistent with data in the
INFORMATION_SCHEMA
PROCESSLIST table or
Performance Schema threads
table.
For example, you should be careful when comparing data in
the InnoDB transaction and locking tables
with data in the PROCESSLIST
table. Even if you issue a single SELECT
(joining INNODB_TRX and
PROCESSLIST, for example), the
content of those tables is generally not consistent. It is
possible for INNODB_TRX to
reference rows that are not present in
PROCESSLIST or for the
currently executing SQL query of a transaction shown in
INNODB_TRX.TRX_QUERY to differ from the
one in PROCESSLIST.INFO.