diff --git a/sql-statements/sql-statement-show-table-regions.md b/sql-statements/sql-statement-show-table-regions.md index 1f0d64432e76..b610b03fdce4 100644 --- a/sql-statements/sql-statement-show-table-regions.md +++ b/sql-statements/sql-statement-show-table-regions.md @@ -58,61 +58,87 @@ SHOW TABLE [table_name] INDEX [index_name] REGIONS [WhereClauseOptional]; ## 示例 +创建一个示例表，并在若干 Region 中填充足够的数据量： + {{< copyable "sql" >}} ```sql -create table t (id int key,name varchar(50), index (name)); -``` - -``` -Query OK, 0 rows affected -``` - -默认新建表后会单独 split 出一个 Region 来存放该表的数据，开始时行数据和索引数据都会写到这个 Region。 +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; +``` + +结果显示示例表被切分成多个 Regions。`REGION_ID`、`START_KEY` 和 `END_KEY` 可能不完全匹配： {{< copyable "sql" >}} ```sql -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 | -+-----------+-----------+---------+-----------+-----------------+-----------+------------+---------------+------------+----------------------+------------------+ -| 3 | t_43_ | | 73 | 9 | 5, 73, 93 | 0 | 35 | 0 | 1 | 0 | -+-----------+-----------+---------+-----------+-----------------+-----------+------------+---------------+------------+----------------------+------------------+ -1 row in set +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) ``` 解释： -- 上面 START_KEY 列的值 t_43_ 中，t 是表数据的前缀，43 是表 t 的 table ID。 -- END_KEY 列的值为空（""）表示无穷大。 +上面 START_KEY 列的值 `t_75_r_31717` 和 END_KEY 列的值 `t_75_r_63434` 表示主键在 `31717` 和 `63434` 之间的数据存储在该 Region 中。`t_75_` 是前缀，表示这是表格 (`t`) 的 Region，`75` 是表格的内部 ID。若 `START_KEY` 或 `END_KEY` 的一对键值为空，分别表示负无穷大或正无穷大。 -用 `SPLIT TABLE REGION` 语法切分行数据的 Region，下面语法把表 t 的行数据切分成 5 个 Region。 +TiDB 会根据需要自动重新平衡 Regions。建议使用 `SPLIT TABLE REGION` 语句手动进行平衡： {{< copyable "sql" >}} ```sql -split table t between (0) and (100000) regions 5; +SPLIT TABLE t1 BETWEEN (31717) AND (63434) REGIONS 2; ``` ``` +--------------------+----------------------+ | TOTAL_SPLIT_REGION | SCATTER_FINISH_RATIO | +--------------------+----------------------+ -| 5 | 1.0 | +| 1 | 1 | +--------------------+----------------------+ -1 row in set +1 row in set (42.34 sec) +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) ``` -解释： +上面的输出结果显示 Region 96 被切分，并创建一个新的 Region 98。切分操作不会影响表中的其他 Region。输出结果同样证实： -- TOTAL_SPLIT_REGION 表示新切的 region 数量，这是新切了 5 个 region. -- SCATTER_FINISH_RATIO 表示新切的 region 的打散成功率，1.0 表示都已经打散了。 +- TOTAL_SPLIT_REGION 表示新切的 Region 数量。以上示例新切了 1 个 Region。 +- SCATTER_FINISH_RATIO 表示新切的 Region 的打散成功率，1.0 表示都已经打散了。 -表 t 现在一共有 6 个 Region，其中 102、106、110、114、3 用来存行数据，Region 98 用来存索引数据。 +更详细的示例如下： {{< copyable "sql" >}} @@ -195,6 +221,10 @@ show table t regions; 7 rows in set ``` +## MySQL 兼容性 + +`SHOW TABLE REGIONS` 语句是 TiDB 对 MySQL 语法的扩展。 + ## 另请参阅 * [SPLIT REGION](/sql-statements/sql-statement-split-region.md)