Tidb implementation plan -- I

mysql> desc select a.name,a.age from student a inner join student2 b on a.age=b.age where a.age < 30;
+-----------------------------+-----------+-----------+-----------------------------+-------------------------------------------------------------+
| id                          | estRows   | task      | access object               | operator info                                               |
+-----------------------------+-----------+-----------+-----------------------------+-------------------------------------------------------------+
| HashJoin_23                 | 29029.00  | root      |                             | inner join, equal:[eq(test.student2.age, test.student.age)] |
| ├─IndexReader_28(Build)     | 29029.00  | root      |                             | index:IndexRangeScan_27                                     |
| │ └─IndexRangeScan_27       | 29029.00  | cop[tikv] | table:b, index:idx_age(age) | range:[-inf,30), keep order:false                           |
| └─TableReader_26(Probe)     | 33294.82  | root      |                             | data:Selection_25                                           |
|   └─Selection_25            | 33294.82  | cop[tikv] |                             | lt(test.student.age, 30), not(isnull(test.student.age))     |
|     └─TableFullScan_24      | 100185.00 | cop[tikv] | table:a                     | keep order:false                                            |
+-----------------------------+-----------+-----------+-----------------------------+-------------------------------------------------------------+
6 rows in set (0.00 sec)

• id： operator _id form , Different operators mean different things ; id Is the only one. ;
• estRows： Number of scan lines estimated from Statistics ;
• task： Operator belongs to task The type of , root task It means that tidb server Operator executed in , cop[tikv] It means that tikv The operator executed by the node , cop[tiflash] It means that tiflash Operator to execute ;
• access object： The data accessed by the operator is like information , Including table table, Table partitioning partition, And the index used index; Only operators that directly access the data have this information
• operator info:  Other description information of the operator , Such as lt(test.student.age,30) Means filter less than Less than or equal to student surface age Field 30 The data of ;

EXPLAIN ANALYZE ...

mysql> explain analyze select a.name,a.age from student a inner join student2 b on a.age=b.age where a.age < 30\G
*************************** 1. row ***************************
            id: HashJoin_21
       estRows: 29029.00
       actRows: 58058
          task: root
 access object: 
execution info: time:12ms, loops:58, build_hash_table:{total:1.17ms, fetch:1.14ms, build:31.8µs}, probe:{concurrency:5, total:57.9ms, max:11.9ms, probe:50.3ms, fetch:7.57ms}
 operator info: inner join, equal:[eq(test.student.age, test.student2.age)]
        memory: 24.5 KB
          disk: 0 Bytes
*************************** 2. row ***************************
            id: ├─TableReader_24(Build)
       estRows: 25654.88
       actRows: 58
          task: root
 access object: 
execution info: time:1.07ms, loops:2, cop_task: {num: 1, max: 1.22ms, proc_keys: 0, rpc_num: 1, rpc_time: 1.19ms, copr_cache_hit_ratio: 1.00}
 operator info: data:Selection_23
        memory: 2.09 KB
          disk: N/A
*************************** 3. row ***************************
            id: │ └─Selection_23
       estRows: 25654.88
       actRows: 58
          task: cop[tikv]
 access object: 
execution info: tikv_task:{time:110ms, loops:102}
 operator info: lt(test.student.age, 30), not(isnull(test.student.age))
        memory: N/A
          disk: N/A
*************************** 4. row ***************************
            id: │   └─TableFullScan_22
       estRows: 100185.00
       actRows: 100098
          task: cop[tikv]
 access object: table:a
execution info: tikv_task:{time:104ms, loops:102}
 operator info: keep order:false
        memory: N/A
          disk: N/A
*************************** 5. row ***************************
            id: └─IndexReader_26(Probe)
       estRows: 29029.00
       actRows: 29029
          task: root
 access object: 
execution info: time:1.47ms, loops:30, cop_task: {num: 1, max: 1.12ms, proc_keys: 0, rpc_num: 1, rpc_time: 1.1ms, copr_cache_hit_ratio: 1.00}
 operator info: index:IndexRangeScan_25
        memory: 227.4 KB
          disk: N/A
*************************** 6. row ***************************
            id:   └─IndexRangeScan_25
       estRows: 29029.00
       actRows: 29029
          task: cop[tikv]
 access object: table:b, index:idx_age(age)
execution info: tikv_task:{time:30ms, loops:33}
 operator info: range:[-inf,30), keep order:false
        memory: N/A
          disk: N/A
6 rows in set (0.02 sec)

• estRows: Estimated number of rows based on Statistics ;
• actRows: Number of rows actually scanned
• execution info： Operator actual execution information ,time Represents the actual execution time of the operator ; If the operator is called more than once loops, This time is the cumulative time ; loops Indicates the number of calls ;
• memory : The amount of memory space occupied by the operator
• disk: The amount of disk space occupied by the operator