The Ultimate Guide to High Availability with MariaDB

Performance Schema threads Table

Each server thread is represented as a row in the threads table.

The threads table contains the following columns:

ColumnDescription
THREAD_IDA unique thread identifier.
NAMEName associated with the server's thread instrumentation code, for example thread/sql/main for the server's main() function, and thread/sql/one_connection for a user connection.
TYPEFOREGROUND or BACKGROUND, depending on the thread type. User connection threads are FOREGROUND, internal server threads are BACKGROUND.
PROCESSLIST_IDThe PROCESSLIST.ID value for threads displayed in the INFORMATION_SCHEMA.PROCESSLIST table, or 0 for background threads. Also corresponds with the CONNECTION_ID() return value for the thread.
PROCESSLIST_USERForeground thread user, or NULL for a background thread.
PROCESSLIST_HOSTForeground thread host, or NULL for a background thread.
PROCESSLIST_DBThread's default database, or NULL if none exists.
PROCESSLIST_COMMANDType of command executed by the thread. These correspond to the the COM_xxx client/server protocol commands, and the Com_xxx status variables. See Thread Command Values.
PROCESSLIST_TIMETime in seconds the thread has been in its current state.
PROCESSLIST_STATEAction, event or state indicating what the thread is doing.
PROCESSLIST_INFOStatement being executed by the thread, or NULL if a statement is not being executed. If a statement results in calling other statements, such as for a stored procedure, the innermost statement from the stored procedure is shown here.
PARENT_THREAD_IDTHREAD_ID of the parent thread, if any. Subthreads can for example be spawned as a result of INSERT DELAYED statements.
ROLEUnused.
INSTRUMENTEDYES or NO for Whether the thread is instrumented or not. For foreground threads, the initial value is determined by whether there's a user/host match in the setup_actors table. Subthreads are again matched, while for background threads, this will be set to YES by default. To monitor events that the thread executes, INSTRUMENTED must be YES and the thread_instrumentation consumer in the setup_consumers table must also be YES.
HISTORYYES or NO for Whether to log historical events for the thread. For foreground threads, the initial value is determined by whether there's a user/host match in the setup_actors table. Subthreads are again matched, while for background threads, this will be set to YES by default. To monitor events that the thread executes, INSTRUMENTED must be YES and the thread_instrumentation consumer in the setup_consumers table must also be YES. Added in MariaDB 10.5.
CONNECTION_TYPEThe protocol used to establish the connection. One of TCP/IP, SSL/TLS, Socket, Named Pipe, Shared Memory, or NULL for background threads. Added in MariaDB 10.5.
THREAD_OS_IDThe thread or task identifier as defined by the underlying operating system, if there is one. Added in MariaDB 10.5

Example

SELECT * FROM performance_schema.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: 215859
  PROCESSLIST_STATE: Table lock
   PROCESSLIST_INFO: INTERNAL DDL LOG RECOVER IN PROGRESS
   PARENT_THREAD_ID: NULL
               ROLE: NULL
       INSTRUMENTED: YES
...
*************************** 21. row ***************************
          THREAD_ID: 64
               NAME: thread/sql/one_connection
               TYPE: FOREGROUND
     PROCESSLIST_ID: 44
   PROCESSLIST_USER: root
   PROCESSLIST_HOST: localhost
     PROCESSLIST_DB: NULL
PROCESSLIST_COMMAND: Query
   PROCESSLIST_TIME: 0
  PROCESSLIST_STATE: Sending data
   PROCESSLIST_INFO: SELECT * FROM performance_schema.threads
   PARENT_THREAD_ID: NULL
               ROLE: NULL
       INSTRUMENTED: YES

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