SHOW TABLE REGIONS

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

Syntax

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

Synopsis

ShowTableRegionStmt
SHOWTABLETableNamePartitionNameListINDEXIndexNameREGIONSWHEREExpression
TableName
SchemaName.Identifier

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.
  • SCHEDULING_STATE: The scheduling state of the Region which has a placement policy.

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 | SCHEDULING_CONSTRAINTS | SCHEDULING_STATE | +-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+------------------------+------------------+ | 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 | SCHEDULING_CONSTRAINTS | SCHEDULING_STATE | +-----------+--------------+--------------+-----------+-----------------+-------+------------+---------------+------------+----------------------+------------------+------------------------+------------------+ | 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 | SCHEDULING_CONSTRAINTS | SCHEDULING_STATE | +-----------+--------------+--------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+------------------------+------------------+ | 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 (106, 110, 114, 3) 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 | SCHEDULING_CONSTRAINTS | SCHEDULING_STATE | +-----------+-----------+---------+-----------+-----------------+--------------+------------+---------------+------------+----------------------+------------------+------------------------+------------------+ | 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 | SCHEDULING_CONSTRAINTS | SCHEDULING_STATE | +-----------+-----------------------------+-----------------------------+-----------+-----------------+---------------+------------+---------------+------------+----------------------+------------------+------------------------+------------------+ | 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

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