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Performance Schema threads Table

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

The threads table contains the following columns:

Column	Description	Added
`THREAD_ID`	A unique thread identifier.	MariaDB 5.5
`NAME`	Name 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.	MariaDB 5.5
`TYPE`	`FOREGROUND` or `BACKGROUND`, depending on the thread type. User connection threads are `FOREGROUND`, internal server threads are `BACKGROUND`.	MariaDB 10.0
`PROCESSLIST_ID`	The `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.	MariaDB 5.5
`PROCESSLIST_USER`	Foreground thread user, or `NULL` for a background thread.	MariaDB 10.0
`PROCESSLIST_HOST`	Foreground thread host, or `NULL` for a background thread.	MariaDB 10.0
`PROCESSLIST_DB`	Thread's default database, or `NULL` if none exists.	MariaDB 10.0
`PROCESSLIST_COMMAND`	Type 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.	MariaDB 10.0
`PROCESSLIST_TIME`	Time in seconds the thread has been in its current state.	MariaDB 10.0
`PROCESSLIST_STATE`	Action, event or state indicating what the thread is doing.	MariaDB 10.0
`PROCESSLIST_INFO`	Statement 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.	MariaDB 10.0
`PARENT_THREAD_ID`	`THREAD_ID` of the parent thread, if any. Subthreads can for example be spawned as a result of INSERT DELAYED statements.	MariaDB 10.0
`ROLE`	Unused.	MariaDB 10.0
`INSTRUMENTED`	`YES` 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`.	MariaDB 10.0

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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https://mariadb.com/kb/en/performance-schema-threads-table/