PROCESSLIST
PROCESSLIST 和 SHOW PROCESSLIST 的功能一样，都是查看当前正在处理的请求。
PROCESSLIST 表比 SHOW PROCESSLIST 的结果多出下面几列：
DIGEST列：显示 SQL 语句的 digest。MEM列：显示正在处理的请求已使用的内存，单位是 byte。DISK列：显示磁盘空间使用情况，单位是 byte。TxnStart列：显示事务的开始时间。RESOURCE_GROUP列：显示对应的资源组名称。
USE information_schema;
DESC processlist;
+---------------------+---------------------+------+------+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------------+---------------------+------+------+---------+-------+
| ID | bigint(21) unsigned | NO | | 0 | |
| USER | varchar(16) | NO | | | |
| HOST | varchar(64) | NO | | | |
| DB | varchar(64) | YES | | NULL | |
| COMMAND | varchar(16) | NO | | | |
| TIME | int(7) | NO | | 0 | |
| STATE | varchar(7) | YES | | NULL | |
| INFO | longtext | YES | | NULL | |
| DIGEST | varchar(64) | YES | | | |
| MEM | bigint(21) unsigned | YES | | NULL | |
| DISK | bigint(21) unsigned | YES | | NULL | |
| TxnStart | varchar(64) | NO | | | |
| RESOURCE_GROUP | varchar(32) | NO | | | |
+---------------------+---------------------+------+------+---------+-------+
13 rows in set (0.00 sec)
SELECT * FROM processlist\G
*************************** 1. row ***************************
ID: 2300033189772525975
USER: root
HOST: 127.0.0.1:51289
DB: NULL
COMMAND: Query
TIME: 0
STATE: autocommit
INFO: SELECT * FROM processlist
DIGEST: dbfaa16980ec628011029f0aaf0d160f4b040885240dfc567bf760d96d374f7e
MEM: 0
DISK: 0
TxnStart:
RESOURCE_GROUP: rg1
1 row in set (0.00 sec)
PROCESSLIST 表各列的含义如下：
ID列：客户连接 ID。USER列：执行当前 PROCESS 的用户名。HOST列：客户连接的地址。DB列：当前连接的默认数据库名。COMMAND列：当前 PROCESS 执行的命令类型。TIME列：当前 PROCESS 的已经执行的时间，单位是秒。STATE列：当前连接的状态。INFO列：正在处理的请求语句。DIGEST列：SQL 语句的 digest。MEM列：正在处理的请求已使用的内存，单位是 byte。DISK列：磁盘空间使用情况，单位是 byte。TxnStart列：显示事务的开始时间。RESOURCE_GROUP列：显示对应的资源组名称。
CLUSTER_PROCESSLIST
CLUSTER_PROCESSLIST 是 PROCESSLIST 对应的集群系统表，用于查询集群中所有 TiDB 节点的 PROCESSLIST 信息。CLUSTER_PROCESSLIST 表结构上比 PROCESSLIST 多一列 INSTANCE，表示该行数据来自的 TiDB 节点地址。
SELECT * FROM cluster_processlist;
+-----------------+-----+------+----------+------+---------+------+------------+------------------------------------------------------+-----+----------------------------------------+----------------+
| INSTANCE | ID | USER | HOST | DB | COMMAND | TIME | STATE | INFO | MEM | TxnStart | RESOURCE_GROUP |
+-----------------+-----+------+----------+------+---------+------+------------+------------------------------------------------------+-----+----------------------------------------+----------------+
| 10.0.1.22:10080 | 150 | u1 | 10.0.1.1 | test | Query | 0 | autocommit | select count(*) from usertable | 372 | 05-28 03:54:21.230(416976223923077223) | default |
| 10.0.1.22:10080 | 138 | root | 10.0.1.1 | test | Query | 0 | autocommit | SELECT * FROM information_schema.cluster_processlist | 0 | 05-28 03:54:21.230(416976223923077220) | rg1 |
| 10.0.1.22:10080 | 151 | u1 | 10.0.1.1 | test | Query | 0 | autocommit | select count(*) from usertable | 372 | 05-28 03:54:21.230(416976223923077224) | rg2 |
| 10.0.1.21:10080 | 15 | u2 | 10.0.1.1 | test | Query | 0 | autocommit | select max(field0) from usertable | 496 | 05-28 03:54:21.230(416976223923077222) | default |
| 10.0.1.21:10080 | 14 | u2 | 10.0.1.1 | test | Query | 0 | autocommit | select max(field0) from usertable | 496 | 05-28 03:54:21.230(416976223923077225) | default |
+-----------------+-----+------+----------+------+---------+------+------------+------------------------------------------------------+-----+----------------------------------------+----------------+