文档目录

SHOW TABLE REGIONS

SHOW TABLE REGIONS 语句用于显示 TiDB 中某个表的 Region 信息。

语法图

SHOW TABLE [table_name] REGIONS [WhereClauseOptional];

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

SHOW TABLE REGIONS 会返回如下列:

  • REGION_ID:Region 的 ID。
  • START_KEY:Region 的 Start key。
  • END_KEY:Region 的 End key。
  • LEADER_ID:Region 的 Leader ID。
  • LEADER_STORE_ID:Region leader 所在的 store (TiKV) ID。
  • PEERS:Region 所有副本的 ID。
  • SCATTERING:Region 是否正在调度中。1 表示正在调度。
  • WRITTEN_BYTES:估算的 Region 在 1 个心跳周期内的写入数据量大小,单位是 byte。
  • READ_BYTES:估算的 Region 在 1 个心跳周期内的读数据量大小,单位是 byte。
  • APPROXIMATE_SIZE(MB):估算的 Region 的数据量大小,单位是 MB。
  • APPROXIMATE_KEYS:估算的 Region 内 Key 的个数。

注意:

WRITTEN_BYTESREAD_BYTESAPPROXIMATE_SIZE(MB)APPROXIMATE_KEYS 的值是 PD 根据 Region 的心跳汇报信息统计,估算出来的数据,所以不是精确的数据。

示例

创建一个示例表,并在若干 Region 中填充足够的数据量:

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_IDSTART_KEYEND_KEY 可能不完全匹配:

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 STARTKEY 列的值 t_75_r_31717 和 END_KEY 列的值 t_75_r_63434 表示主键在 3171763434 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_KEYEND_KEY` 的一对键值为空,分别表示负无穷大或正无穷大。

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:

SPLIT TABLE t1 BETWEEN (31717) AND (63434) REGIONS 2;
+--------------------+----------------------+
| TOTAL_SPLIT_REGION | SCATTER_FINISH_RATIO |
+--------------------+----------------------+
|                  1 |                    1 |
+--------------------+----------------------+
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)

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。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。

更详细的示例如下:

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

解释:

  • Region 102 的 START_KEY 和 END_KEY 中,t_43 是表数据前缀和 table ID,_r 是表 t record 数据的前缀,索引数据的前缀是 _i,所以 Region 102 的 START_KEY 和 END_KEY 表示用来存储 [-inf, 20000) 之前的 record 数据。其他 Region (103, 109, 113, 2) 的存储范围依次类推。
  • Region 98 用来存储索引数据存储。表 t 索引数据的起始 key 是 t_43_i,处于 Region 98 的存储范围内。

查看表 t 在 store 1 上的 region,用 where 条件过滤。

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                |
+-----------+-----------+---------+-----------+-----------------+--------------+------------+---------------+------------+----------------------+------------------+

SPLIT TABLE REGION 语法切分索引数据的 Region,下面语法把表 t 的索引 name 数据在 [a,z] 范围内切分成 2 个 Region。

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

现在表 t 一共有 7 个 Region,其中 5 个 Region (102, 106, 110, 114, 3) 用来存表 t 的 record 数据,另外 2 个 Region (135, 98) 用来存 name 索引的数据。

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 兼容性

SHOW TABLE REGIONS 语句是 TiDB 对 MySQL 语法的扩展。

另请参阅