--- title: "并行 DML - OceanBase 数据库 V4.2.0 | OceanBase 文档中心" description: 并行 DML 并行 DML 通过使用并行执行机制来提高对大型数据库的表和索引执行插入、更新、删除等操作，以提高执行效率。对于决策支持系统 (DSS)的数据库，并行 DML 提供了查询和更新功能，是对并行查询功能的补充。对于 OLTP 数据库，并行 DML 操作可以加速批处理作业的运行。 开启和关闭并行 DML Oce… --- 切换语言 - 中文站 - 简体中文 - International - English - 日本站 - 日本語 文档反馈![](https://mdn.alipayobjects.com/huamei_22khvb/afts/img/A*P8CuR4UJ_FkAAAAAAAAAAAAADiGDAQ/original) OceanBase 数据库分布式版 - V 4.2.0 # 并行 DML 更新时间：2025-05-26 12:16:04 [编辑](https://github.com/oceanbase/oceanbase-doc/edit/V4.2.0/zh-CN/700.reference/1000.performance-tuning-guide/500.sql-optimization/300.distributed-execution-plan/1000.parallel-dml.md) 并行 DML 通过使用并行执行机制来提高对大型数据库的表和索引执行插入、更新、删除等操作，以提高执行效率。对于决策支持系统 (DSS)的数据库，并行 DML 提供了查询和更新功能，是对并行查询功能的补充。对于 OLTP 数据库，并行 DML 操作可以加速批处理作业的运行。 ## 开启和关闭并行 DML OceanBase 数据库支持在 SQL 语句或会话中显式启用并行 DML。 ### 在 SQL 语句中启用和关闭并行 DML 在 SQL 语句中启用并行 DML，请在语句中插入如下 Hint： ```sql /*+ ENABLE_PARALLEL_DML PARALLEL(3) */ ``` 一般情况下，`ENABLE_PARALLEL_DML` Hint 和 `PARALLEL` Hint 必须配合使用才能开启并行 DML。不过，当目标表的 Schema 上指定了表级别的并行度时，仅需指定 `ENABLE_PARALLEL_DML` Hint。 如下示例为同时使用 `ENABLE_PARALLEL_DML` Hint 和 `PARALLEL(n)` 参数指定并行度 `n`，并且 `n > 1`，并行度 `dop=2`。 ```sql CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT) NOPARALLEL; CREATE TABLE t2 (c1 INT PRIMARY KEY, c2 INT) PARALLEL 11 PARTITION BY HASH(c1) PARTITIONS 3; CREATE TABLE t3 (c1 INT PRIMARY KEY, c2 INT) PARALLEL 10 PARTITION BY HASH(c1) PARTITIONS 4; obclient> EXPLAIN INSERT /*+ ENABLE_PARALLEL_DML PARALLEL(2) */ INTO t1 SELECT * FROM T3; +-------------------------------------------------------------------------------------------------------------------------------------------------------+ | Query Plan | +-------------------------------------------------------------------------------------------------------------------------------------------------------+ | ========================================================================= | | |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| | | ------------------------------------------------------------------------- | | |0 |OPTIMIZER STATS MERGE | |1 |18 | | | |1 | PX COORDINATOR | |1 |18 | | | |2 | EXCHANGE OUT DISTR |:EX10001 |1 |18 | | | |3 | INSERT | |1 |17 | | | |4 | EXCHANGE IN DISTR | |1 |4 | | | |5 | EXCHANGE OUT DISTR (HASH)|:EX10000 |1 |4 | | | |6 | OPTIMIZER STATS GATHER | |1 |4 | | | |7 | SUBPLAN SCAN |ANONYMOUS_VIEW1|1 |4 | | | |8 | PX BLOCK ITERATOR | |1 |4 | | | |9 | TABLE SCAN |t3 |1 |4 | | | ========================================================================= | | Outputs & filters: | | ------------------------------------- | | 0 - output(nil), filter(nil), rowset=256 | | 1 - output([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]), filter(nil), rowset=256 | | 2 - output([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]), filter(nil), rowset=256 | | dop=2 | | 3 - output([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]), filter(nil) | | columns([{t1: ({t1: (t1.c1, t1.c2)})}]), partitions(p0), | | column_values([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]) | | 4 - output([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]), filter(nil), rowset=256 | | 5 - output([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]), filter(nil), rowset=256 | | (#keys=1, [column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)]), dop=2 | | 6 - output([column_conv(INT,PS:(11,0),NOT NULL,ANONYMOUS_VIEW1.c1)], [column_conv(INT,PS:(11,0),NULL,ANONYMOUS_VIEW1.c2)]), filter(nil), rowset=256 | | 7 - output([ANONYMOUS_VIEW1.c1], [ANONYMOUS_VIEW1.c2]), filter(nil), rowset=256 | | access([ANONYMOUS_VIEW1.c1], [ANONYMOUS_VIEW1.c2]) | | 8 - output([t3.c1], [t3.c2]), filter(nil), rowset=256 | | 9 - output([t3.c1], [t3.c2]), filter(nil), rowset=256 | | access([t3.c1], [t3.c2]), partitions(p[0-3]) | | is_index_back=false, is_global_index=false, | | range_key([t3.c1]), range(MIN ; MAX)always true | +-------------------------------------------------------------------------------------------------------------------------------------------------------+ 34 rows in set ``` 如果要禁用并行 DML，请在语句中插入如下 Hint： ```sql /*+ DISABLE_PARALLEL_DML */ ``` 即使会话中启用了并行 DML，您也可以在指定 SQL 语句中使用 `DISABLE_PARALLEL_DML` Hint 禁用并行 DML。 ### 在会话中启用和关闭并行 DML 默认情况下，即使 SQL语句中使用了 `PARALLEL` Hint，并行 DML 也是不开启的，所以还需要通过在会话上开启并行 DML。 在会话中启用并行 DML，MySQL 模式下语法为： ```sql SET _FORCE_PARALLEL_DML_DOP = n; ``` 其中 n 大于 1。 在会话中启用并行 DML，Oracle 模式下语法为： ```sql ALTER SESSION ENABLE PARALLEL DML; ``` Oracle 模式下，如果需要在会话中强制开启并行 DML，请运行以下 SQL 语句： ```sql ALTER SESSION FORCE PARALLEL DML PARALLEL n; ``` 如下示例为，Oracle 模式下在会话中强制开启并行 DML。 ```sql CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT) NOPARALLEL; CREATE TABLE t2 (c1 INT PRIMARY KEY, c2 INT) PARALLEL 11 PARTITION BY HASH(c1) PARTITIONS 3; CREATE TABLE t3 (c1 INT PRIMARY KEY, c2 INT) PARALLEL 10 PARTITION BY HASH(c1) PARTITIONS 4; obclient> ALTER SESSION FORCE PARALLEL DML PARALLEL 6; Query OK, 0 rows affected obclient> EXPLAIN INSERT INTO t2 SELECT * FROM t3; +------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | ============================================================================== | | |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| | | ------------------------------------------------------------------------------ | | |0 |OPTIMIZER STATS MERGE | |1 |16 | | | |1 | PX COORDINATOR | |1 |16 | | | |2 | EXCHANGE OUT DISTR |:EX10001 |1 |15 | | | |3 | INSERT | |1 |15 | | | |4 | EXCHANGE IN DISTR | |1 |2 | | | |5 | EXCHANGE OUT DISTR (PKEY HASH)|:EX10000 |1 |2 | | | |6 | OPTIMIZER STATS GATHER | |1 |2 | | | |7 | SUBPLAN SCAN |ANONYMOUS_VIEW1|1 |2 | | | |8 | PX BLOCK ITERATOR | |1 |2 | | | |9 | TABLE SCAN |T3 |1 |2 | | | ============================================================================== | | Outputs & filters: | | ------------------------------------- | | 0 - output(nil), filter(nil), rowset=256 | | 1 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil), rowset=256 | | 2 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil), rowset=256 | | dop=6 | | 3 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil) | | columns([{T2: ({T2: (T2.C1, T2.C2)})}]), partitions(p[0-2]), | | column_values([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]) | | 4 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)], [PARTITION_ID]), filter(nil), | | rowset=256 | | 5 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)], [PARTITION_ID]), filter(nil), | | rowset=256 | | (#keys=1, [column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)]), dop=6 | | 6 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil), rowset=256 | | 7 - output([ANONYMOUS_VIEW1.C1], [ANONYMOUS_VIEW1.C2]), filter(nil), rowset=256 | | access([ANONYMOUS_VIEW1.C1], [ANONYMOUS_VIEW1.C2]) | | 8 - output([T3.C1], [T3.C2]), filter(nil), rowset=256 | | 9 - output([T3.C1], [T3.C2]), filter(nil), rowset=256 | | access([T3.C1], [T3.C2]), partitions(p[0-3]) | | is_index_back=false, is_global_index=false, | | range_key([T3.C1]), range(MIN ; MAX)always true | +------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 36 rows in set ``` 需要注意的是，在 SQL 语句中启用并行 DML 时，一般使用由 Hint 指定的并行度来执行查询，其优先级高于会话中强制指定的并行度。Oracle 模式下的示例如下： obclient> EXPLAIN INSERT /*+ PARALLEL(3) */ INTO t2 SELECT * FROM t3; +------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Query Plan | +------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | ============================================================================== | | |ID|OPERATOR |NAME |EST.ROWS|EST.TIME(us)| | | ------------------------------------------------------------------------------ | | |0 |OPTIMIZER STATS MERGE | |1 |17 | | | |1 | PX COORDINATOR | |1 |17 | | | |2 | EXCHANGE OUT DISTR |:EX10001 |1 |17 | | | |3 | INSERT | |1 |16 | | | |4 | EXCHANGE IN DISTR | |1 |3 | | | |5 | EXCHANGE OUT DISTR (PKEY HASH)|:EX10000 |1 |3 | | | |6 | OPTIMIZER STATS GATHER | |1 |3 | | | |7 | SUBPLAN SCAN |ANONYMOUS_VIEW1|1 |3 | | | |8 | PX BLOCK ITERATOR | |1 |3 | | | |9 | TABLE SCAN |T3 |1 |3 | | | ============================================================================== | | Outputs & filters: | | ------------------------------------- | | 0 - output(nil), filter(nil), rowset=256 | | 1 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil), rowset=256 | | 2 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil), rowset=256 | | dop=3 | | 3 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil) | | columns([{T2: ({T2: (T2.C1, T2.C2)})}]), partitions(p[0-2]), | | column_values([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]) | | 4 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)], [PARTITION_ID]), filter(nil), | | rowset=256 | | 5 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)], [PARTITION_ID]), filter(nil), | | rowset=256 | | (#keys=1, [column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)]), dop=3 | | 6 - output([column_conv(NUMBER,PS:(-1,0),NOT NULL,ANONYMOUS_VIEW1.C1)], [column_conv(NUMBER,PS:(-1,0),NULL,ANONYMOUS_VIEW1.C2)]), filter(nil), rowset=256 | | 7 - output([ANONYMOUS_VIEW1.C1], [ANONYMOUS_VIEW1.C2]), filter(nil), rowset=256 | | access([ANONYMOUS_VIEW1.C1], [ANONYMOUS_VIEW1.C2]) | | 8 - output([T3.C1], [T3.C2]), filter(nil), rowset=256 | | 9 - output([T3.C1], [T3.C2]), filter(nil), rowset=256 | | access([T3.C1], [T3.C2]), partitions(p[0-3]) | | is_index_back=false, is_global_index=false, | | range_key([T3.C1]), range(MIN ; MAX)always true | +------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 36 rows in set ``` 如果要禁用并行 DML，MySQL 模式下的 SQL 语句为： ```sql SET _FORCE_PARALLEL_DML_DOP = 1; ``` 如果要禁用并行 DML，Oracle 模式下的 SQL 语句为： ```sql ALTER SESSION DISABLE PARALLEL DML; ``` 禁用并行 DML 时，即使在 SQL 语句中使用 `PARALLEL` Hint，也不会执行并行 DML。 在会话中启用并行 DML 时，则并行执行对此会话中的所有 DML 语句都会生效。如果 SQL 语句通过 `ENABLE_PARALLEL_DML` Hint 启用并行 DML 时，则并行执行仅对指定语句生效。但是，如果没有具有并行属性的表，或者违反了并行操作的限制，即使启用了并行 DML，DML 操作仍然会串行执行。 ## 使用说明 OceanBase 数据库支持如下 SQL 语句的并行执行能力： - `INSERT INTO SELECT` - `UPDATE` - `DELETE` 如果表上存在下列索引类型，则需要支持并行执行： - 局部索引 - 单分区全局索引 - 多分区全局索引 OceanBase 数据库不支持以下 SQL 语句使用并行 DML： - `REPLACE` - `INSERT INTO ON DUPLICATE KEY UPDATE` - 不支持多表 DML 语句 如果表上存在如下属性，也不支持并行 DML： - 触发器 - 外键 - `CHECK` 约束 - 唯一索引 上一篇 下一篇 ![有帮助](https://gw.alipayobjects.com/mdn/ob_asset/afts/img/A*y6ocSqN8cqsAAAAAAAAAAAAAARQnAQ)![无帮助](https://gw.alipayobjects.com/mdn/ob_asset/afts/img/A*BG9IQJyLHF8AAAAAAAAAAAAAARQnAQ)![反馈](https://gw.alipayobjects.com/mdn/ob_asset/afts/img/A*eTWdQKCRKHwAAAAAAAAAAAAAARQnAQ)[AI](https://www.oceanbase.com/obi) 咨询热线