8.14.1 Accessing the Process List
The following discussion enumerates the sources of process information, the privileges required to see process information, and describes the content of process list entries.
Process information is available from these sources:
PROCESSLISTtable: Section 24.18, “The INFORMATION_SCHEMA PROCESSLIST Table”
sessionviews: Section 188.8.131.52, “The processlist and x$processlist Views”, and Section 184.108.40.206, “The session and x$session Views”
Access to the
threadstable does not require a mutex and has minimal impact on server performance. The other sources have negative performance consequences because they require a mutex.
threadstable provides additional information for each thread that the other sources do not, such as whether the thread is a foreground or background thread, and the location within the server associated with the thread. This means that the
threadstable can be used to monitor thread activity the other sources cannot.
You can enable or disable Performance Schema thread monitoring, as described in Section 220.127.116.11, “The threads Table”.
For these reasons, DBAs who perform server monitoring using one of the other thread information sources may wish to monitor using the
threads table instead.
processlist view presents information from the Performance Schema
threads table in a more accessible format. The
session view presents information about user sessions like the
processlist view, but with background processes filtered out.
For most sources of process information, if you have the
PROCESS privilege, you can see all threads, even those belonging to other users. Otherwise (without the
PROCESS privilege), nonanonymous users have access to information about their own threads but not threads for other users, and anonymous users have no access to thread information.
Each process list entry contains several pieces of information. The following list describes them using the labels from
SHOW PROCESSLIST output. Other process information sources use similar labels.
Idis the connection identifier for the client associated with the thread.
Hostindicate the account associated with the thread.
dbis the default database for the thread, or
NULLif none has been selected.
Stateindicate what the thread is doing.
Most states correspond to very quick operations. If a thread stays in a given state for many seconds, there might be a problem that needs to be investigated.
The following sections list the possible
Statevalues grouped by category. The meaning for some of these values is self-evident. For others, additional description is provided.Note
Applications that examine process list information should be aware that the commands and states are subject to change.
Timeindicates how long the thread has been in its current state. The thread's notion of the current time may be altered in some cases: The thread can change the time with
SET TIMESTAMP =. For a replica SQL thread, the value is the number of seconds between the timestamp of the last replicated event and the real time of the replica host. See Section 16.2.2, “Replication Implementation Details”.
Infoindicates the statement the thread is executing, or
NULLif it is executing no statement. For
SHOW PROCESSLIST, this value contains only the first 100 characters of the statement. To see complete statements, use
SHOW FULL PROCESSLIST(or query a diffferent process information source).