SHOW TABLE REGIONS

The SHOW TABLE REGIONS statement is used to show the Region information of a table in TiDB.

Synopsis

SHOW TABLE [table_name] REGIONS [WhereClauseOptional];
SHOW TABLE [table_name] INDEX [index_name] REGIONS [WhereClauseOptional];

Executing SHOW TABLE REGIONS returns the following columns:

• REGION_ID: The Region ID.
• START_KEY: The start key of the Region.
• END_KEY: The end key of the Region.
• LEADER_ID: The Leader ID of the Region.
• LEADER_STORE_ID: The ID of the store (TiKV) where the Region leader is located.
• PEERS: The IDs of all Region replicas.
• SCATTERING: Whether the Region is being scheduled. 1 means true.
• WRITTEN_BYTES: The estimated amount of data written into the Region within one heartbeat cycle. The unit is byte.
• READ_BYTES: The estimated amount of data read from the Region within one heartbeat cycle. The unit is byte.
• APPROXIMATE_SIZE(MB): The estimated amount of data in the Region. The unit is megabytes (MB).
• APPROXIMATE_KEYS: The estimated number of Keys in the Region.

Examples

Create an example table with enough data that fills a few Regions:

CREATE TABLE t1 (
 id INT NOT NULL PRIMARY KEY auto_increment,
 b INT NOT NULL,
 pad1 VARBINARY(1024),
 pad2 VARBINARY(1024),
 pad3 VARBINARY(1024)
);
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM dual;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(1024), RANDOM_BYTES(1024), RANDOM_BYTES(1024) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 10000;
SELECT SLEEP(5);
SHOW TABLE t1 REGIONS;

The output should show that the table is split into Regions. The REGION_ID, START_KEY and END_KEY may not match exactly:

...
mysql> SHOW TABLE t1 REGIONS;
+-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+
| REGION_ID | START_KEY    | END_KEY      | LEADER_ID | LEADER_STORE_ID | PEERS | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |
+-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+
|        94 | t_75_        | t_75_r_31717 |        95 |               1 | 95    |          0 |             0 |          0 |                  112 |           207465 |
|        96 | t_75_r_31717 | t_75_r_63434 |        97 |               1 | 97    |          0 |             0 |          0 |                   97 |                0 |
|         2 | t_75_r_63434 |              |         3 |               1 | 3     |          0 |     269323514 |   66346110 |                  245 |           162020 |
+-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+
3 rows in set (0.00 sec)

In the output above, a START_KEY of t_75_r_31717 and END_KEY of t_75_r_63434 shows that data with a PRIMARY KEY between 31717 and 63434 is stored in this Region. The prefix t_75_ indicates that this is the Region for a table (t) which has an internal table ID of 75. An empty key value for START_KEY or END_KEY indicates negative infinity or positive infinity respectively.

TiDB automatically rebalances Regions as needed. For manual rebalancing, use the SPLIT TABLE REGION statement:

mysql> SPLIT TABLE t1 BETWEEN (31717) AND (63434) REGIONS 2;
+--------------------+----------------------+
| TOTAL_SPLIT_REGION | SCATTER_FINISH_RATIO |
+--------------------+----------------------+
|                  1 |                    1 |
+--------------------+----------------------+
1 row in set (42.34 sec)

mysql> SHOW TABLE t1 REGIONS;
+-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+
| REGION_ID | START_KEY    | END_KEY      | LEADER_ID | LEADER_STORE_ID | PEERS | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |
+-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+
|        94 | t_75_        | t_75_r_31717 |        95 |               1 | 95    |          0 |             0 |          0 |                  112 |           207465 |
|        98 | t_75_r_31717 | t_75_r_47575 |        99 |               1 | 99    |          0 |          1325 |          0 |                   53 |            12052 |
|        96 | t_75_r_47575 | t_75_r_63434 |        97 |               1 | 97    |          0 |          1526 |          0 |                   48 |                0 |
|         2 | t_75_r_63434 |              |         3 |               1 | 3     |          0 |             0 |   55752049 |                   60 |                0 |
+-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+
4 rows in set (0.00 sec)

The above output shows that Region 96 was split, with a new Region 98 being created. The remaining Regions in the table were unaffected by the split operation. This is confirmed by the output statistics:

• TOTAL_SPLIT_REGION indicates the number of newly split Regions. In this example, the number is 1.
• SCATTER_FINISH_RATIO indicates the rate at which the newly split Regions are successfully scattered. 1.0 means that all Regions are scattered.

For a more detailed example:

mysql> show table t regions;
+-----------+--------------+--------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+
| REGION_ID | START_KEY    | END_KEY      | LEADER_ID | LEADER_STORE_ID | PEERS         | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |
+-----------+--------------+--------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+
| 102       | t_43_r       | t_43_r_20000 | 118       | 7               | 105, 118, 119 | 0          | 0             | 0          | 1                    | 0                |
| 106       | t_43_r_20000 | t_43_r_40000 | 120       | 7               | 107, 108, 120 | 0          | 23            | 0          | 1                    | 0                |
| 110       | t_43_r_40000 | t_43_r_60000 | 112       | 9               | 112, 113, 121 | 0          | 0             | 0          | 1                    | 0                |
| 114       | t_43_r_60000 | t_43_r_80000 | 122       | 7               | 115, 122, 123 | 0          | 35            | 0          | 1                    | 0                |
| 3         | t_43_r_80000 |              | 93        | 8               | 5, 73, 93     | 0          | 0             | 0          | 1                    | 0                |
| 98        | t_43_        | t_43_r       | 99        | 1               | 99, 100, 101  | 0          | 0             | 0          | 1                    | 0                |
+-----------+--------------+--------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+
6 rows in set

In the above example:

• Table t corresponds to six Regions. In these Regions, 102, 106, 110, 114, and 3 store the row data and 98 stores the index data.
• For START_KEY and END_KEY of Region 102, t_43 indicates the table prefix and ID. _r is the prefix of the record data in table t. _i is the prefix of the index data.
• In Region 102, START_KEY and END_KEY mean that record data in the range of [-inf, 20000) is stored. In similar way, the ranges of data storage in Regions (103, 109, 113, 2) can also be calculated.
• Region 98 stores the index data. The start key of table t's index data is t_43_i, which is in the range of Region 98.

To check the Region that corresponds to table t in store 1, use the WHERE clause:

test> show table t regions where leader_store_id =1;
+-----------+-----------+---------+-----------+-----------------+--------------+------------+---------------+------------+----------------------+------------------+
| REGION_ID | START_KEY | END_KEY | LEADER_ID | LEADER_STORE_ID | PEERS        | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |
+-----------+-----------+---------+-----------+-----------------+--------------+------------+---------------+------------+----------------------+------------------+
| 98        | t_43_     | t_43_r  | 99        | 1               | 99, 100, 101 | 0          | 0             | 0          | 1                    | 0                |
+-----------+-----------+---------+-----------+-----------------+--------------+------------+---------------+------------+----------------------+------------------+

Use SPLIT TABLE REGION to split the index data into Regions. In the following example, the index data name of table t is split into two Regions in the range of [a,z].

test> split table t index name between ("a") and ("z") regions 2;
+--------------------+----------------------+
| TOTAL_SPLIT_REGION | SCATTER_FINISH_RATIO |
+--------------------+----------------------+
| 2                  | 1.0                  |
+--------------------+----------------------+
1 row in set

Now table t corresponds to seven Regions. Five of them (102, 106, 110, 114, 3) store the record data of table t and another two (135, 98) store the index data name.

test> show table t regions;
+-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+
| REGION_ID | START_KEY                   | END_KEY                     | LEADER_ID | LEADER_STORE_ID | PEERS         | SCATTERING | WRITTEN_BYTES | READ_BYTES | APPROXIMATE_SIZE(MB) | APPROXIMATE_KEYS |
+-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+
| 102       | t_43_r                      | t_43_r_20000                | 118       | 7               | 105, 118, 119 | 0          | 0             | 0          | 1                    | 0                |
| 106       | t_43_r_20000                | t_43_r_40000                | 120       | 7               | 108, 120, 126 | 0          | 0             | 0          | 1                    | 0                |
| 110       | t_43_r_40000                | t_43_r_60000                | 112       | 9               | 112, 113, 121 | 0          | 0             | 0          | 1                    | 0                |
| 114       | t_43_r_60000                | t_43_r_80000                | 122       | 7               | 115, 122, 123 | 0          | 35            | 0          | 1                    | 0                |
| 3         | t_43_r_80000                |                             | 93        | 8               | 73, 93, 128   | 0          | 0             | 0          | 1                    | 0                |
| 135       | t_43_i_1_                   | t_43_i_1_016d80000000000000 | 139       | 2               | 138, 139, 140 | 0          | 35            | 0          | 1                    | 0                |
| 98        | t_43_i_1_016d80000000000000 | t_43_r                      | 99        | 1               | 99, 100, 101  | 0          | 0             | 0          | 1                    | 0                |
+-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+
7 rows in set

MySQL compatibility

This statement is a TiDB extension to MySQL syntax.

See also

• SPLIT REGION
• CREATE TABLE