threads table contains a row
for each server thread. Each row contains information about a
thread and indicates whether monitoring is enabled for it:
SELECT * FROM threads\G*************************** 1. row *************************** THREAD_ID: 1 NAME: thread/sql/main TYPE: BACKGROUND PROCESSLIST_ID: NULL PROCESSLIST_USER: NULL PROCESSLIST_HOST: NULL PROCESSLIST_DB: NULL PROCESSLIST_COMMAND: NULL PROCESSLIST_TIME: 80284 PROCESSLIST_STATE: NULL PROCESSLIST_INFO: NULL PARENT_THREAD_ID: NULL ROLE: NULL INSTRUMENTED: YES ... *************************** 4. row *************************** THREAD_ID: 51 NAME: thread/sql/one_connection TYPE: FOREGROUND PROCESSLIST_ID: 34 PROCESSLIST_USER: isabella PROCESSLIST_HOST: localhost PROCESSLIST_DB: performance_schema PROCESSLIST_COMMAND: Query PROCESSLIST_TIME: 0 PROCESSLIST_STATE: Sending data PROCESSLIST_INFO: SELECT * FROM threads PARENT_THREAD_ID: 1 ROLE: NULL INSTRUMENTED: YES ...
When the Performance Schema initializes, it populates the
threads table based on the
threads in existence then. Thereafter, a new row is added each
time the server creates a thread.
INSTRUMENTED column value for new
threads is determined by the contents of the
setup_actors table. For
information about how to use the
setup_actors table to control
this column, see
Section 188.8.131.52.3, “Pre-Filtering by Thread”.
Removal of rows from the
table occurs when threads end. For a thread associated with a
client session, removal occurs when the session ends. If a
client has auto-reconnect enabled and the session reconnects
after a disconnect, the session becomes associated with a new
row in the
threads table that has
PROCESSLIST_ID value. The
INSTRUMENTED value for the new
thread may be different from that of the original thread: The
setup_actors table may have
changed in the meantime, and if the
INSTRUMENTED value for the original thread
was changed after it was initialized, that change does not
carry over to the new thread.
threads table columns with
names having a prefix of
provide information similar to that available from the
table or the
statement. Thus, all three sources provide thread-monitoring
information. Use of
differs from use of the other two sources in these ways:
threadsdoes not require a mutex and has minimal impact on server performance.
SHOW PROCESSLISThave negative performance consequences because they require a mutex.
threadsprovides additional information for each thread, such as whether it is a foreground or background thread, and the location within the server associated with the thread.
threadsprovides information about background threads, so it can be used to monitor activity the other thread information sources cannot.
You can enable or disable thread monitoring (that is, whether events executed by the thread are instrumented). To control the initial
INSTRUMENTEDvalue for new foreground threads, use the
setup_actorstable. To control monitoring of existing threads, set the
threadstable rows. (For more information about the conditions under which thread monitoring occurs, see the description of the
information about threads for other users is shown only if
the current user has the
PROCESS privilege. That is
not true of the
all rows are shown to any user who has the
SELECT privilege for the table. Users who
should not be able to see threads for other users should not
be given that privilege.
threads table has these
A unique thread identifier.
The name associated with the thread instrumentation code in the server. For example,
thread/sql/one_connectioncorresponds to the thread function in the code responsible for handling a user connection, and
thread/sql/mainstands for the
main()function of the server.
The thread type, either
BACKGROUND. User connection threads are foreground threads. Threads associated with internal server activity are background threads. Examples are internal
InnoDBthreads, “binlog dump” threads sending information to slaves, and slave I/O and SQL threads.
For threads that are displayed in the
INFORMATION_SCHEMA.PROCESSLISTtable, this is the same value displayed in the
IDcolumn of that table. It is also the value displayed in the
SHOW PROCESSLISToutput, and the value that
CONNECTION_ID()would return within that thread.
For background threads (threads not associated with a user connection),
NULL, so the values are not unique. (Before MySQL 5.6.9, the value is 0 for background threads.)
The user associated with a foreground thread,
NULLfor a background thread.
The host name of the client associated with a foreground thread,
NULLfor a background thread.
The default database for the thread, or
NULLif there is none.
For foreground threads, the type of command the thread is executing on behalf of the client, or
Sleepif the session is idle. For descriptions of thread commands, see Section 8.14, “Examining Thread Information”. The value of this column corresponds to the
COM_commands of the client/server protocol and
Com_status variables. See Section 5.1.6, “Server Status Variables”
Background threads do not execute commands on behalf of clients, so this column may be
The time in seconds that the thread has been in its current state.
An action, event, or state that indicates what the thread is doing. For descriptions of
PROCESSLIST_STATEvalues, see Section 8.14, “Examining Thread Information”. If the value if
NULL, the thread may correspond to an idle client session or the work it is doing is not instrumented with stages.
Most states correspond to very quick operations. If a thread stays in a given state for many seconds, there might be a problem that bears investigation.
The statement the thread is executing, or
NULLif it is not executing any statement. The statement might be the one sent to the server, or an innermost statement if the statement executes other statements. For example, if a
CALLstatement executes a stored procedure that is executing a
PROCESSLIST_INFOvalue shows the
If this thread is a subthread (spawned by another thread), this is the
THREAD_IDvalue of the spawning thread. Thread spawning occurs, for example, to handle insertion of rows from
Whether events executed by the thread are instrumented. The value is
For foreground threads, the initial
INSTRUMENTEDvalue is determined by whether the user account associated with the thread matches any row in the
setup_actorstable. Matching is based on the values of the
If the thread spawns a subthread, matching occurs again for the
threadstable row created for the subthread.
For background threads,
setup_actorsis not consulted because there is no associated user for background threads.
For any thread, its
INSTRUMENTEDvalue can be changed during the lifetime of the thread. This is the only
threadstable column that can be modified.
For monitoring of events executed by the thread to occur, these things must be true: