Select /*+parallel(tab n)*/ from tab; Alter session force parallel query parallel n; 如果没有设置将执行默认并行度 3. 默认并行度 单实例 = PARALLEL_THREADS_PER_CPU x CPU_COUNT RAC = PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT SQL> show parameter parallel NAME TYPE VALUE --- ...
当一条SQL语句发生全表扫描、全分区扫描及索引快速全扫描的时候,若优化器满足下面的条件之一就可以使用并行处理: ① 会话级别,会话设置了强制并行,例如,“ALTER SESSION FORCE PARALLEL QUERY PARALLEL 4;”,执行“SELECT COUNT(*) FROM TB_PART_LHR;”,这里的TB_PART_LHR为分区表。 ② 语句级别,SQL语句中有Hin...
no parallel plan is generated. For example, a cursor created using DECLARE CURSOR will never use a parallel plan. Similarly, a PL/pgSQL loop of the form FOR x IN query LOOP … END LOOP will never use a parallel plan, because the parallel...
Select /*+parallel(tab n)*/ from tab; Alter session force parallel query parallel n; 如果没有设置将执行默认并行度 3. 默认并行度 单实例 = PARALLEL_THREADS_PER_CPU x CPU_COUNT RAC = PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT SQL> show parameter parallel NAME TYPE VALUE --- ...
Alter session force parallel query parallel n; 如果没有设置将执行默认并行度 3. 默认并行度 单实例 = PARALLEL_THREADS_PER_CPU x CPU_COUNT RAC = PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT SQL> show parameter parallel NAME TYPE VALUE ...
The optimizer might make a different choice when the query is actually run, if the situation changed in the meantime. For example, EXPLAIN might report that a statement will use parallel query. But when the query is actually run later, it might not use parallel query based on the conditions...
The PostgreSQL documentation has achapter on the limitations of parallel query. For example, most data modifying statements don't support parallel query. Also, queries that usePARALLEL UNSAFEfunctions or are executed in a cursor cannot use parallel query. But none of these limitations can affect us...
For these queries, SQL Server inserts exchange operators into the query execution plan to prepare the query for parallel execution. An exchange operator is an operator in a query execution plan that provides process management, data redistribution, and flow control. The exchange operator includes the...
Alter session force parallel query parallel n;如果没有设置将执⾏默认并⾏度 3. 默认并⾏度 单实例 = PARALLEL_THREADS_PER_CPU x CPU_COUNT RAC = PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT SQL> show parameter parallel NAME TYPE VALUE --- --- --- fast_start_parallel_rol...
If processes can run ten times faster, then the system can accomplish ten times more in the original amount of time. The parallel query feature, for example, permits scaleup: a system might maintain the same response time if the data queried increases tenfold, or if more users can be ...