Parallel Query Parameters
In the parallel framework, six parallel parameters are added:
Parameter |
Description |
Value |
|---|---|---|
parallel_cost_threshold |
Global- and session-level parameter, which is used to set the threshold for parallel query of SQL statements. Parallel queries are executed only when the estimated cost of a query is higher than this threshold. When the estimated cost is lower than this threshold, a native query process is executed. |
|
parallel_default_dop |
Global- and session-level parameter, which is used to set the maximum number of parallel queries for each SQL statement. The query parallelism of a SQL statement is dynamically adjusted based on the table size. If the binary tree of the table is too small (the number of table slices is less than the concurrency), set the query concurrency based on the number of table slices. The maximum degree of parallelism for each query does not exceed the value of parallel_default_dop. The value of this parameter cannot be greater than that of parallel_max_threads. Otherwise, parallel query of SQL statements cannot be enabled. |
|
parallel_max_threads |
Global-level parameter, which is used to set the total number of concurrent query threads. |
|
parallel_memory_limit |
Global-level parameter, which is used to set the upper limit of the total memory used by the leader thread and worker threads in parallel execution. |
|
parallel_queue_timeout |
Global- and session-level parameter, which is used to set the timeout interval for parallel queries. If system resources are insufficient, for example, the number of running parallel query threads reaches the value of parallel_max_threads, the parallel query statements will wait for available resources. If no resource is available after timeout, native query is executed. |
|
force_parallel_execute |
Global- and session-level parameter, which is used to set the switch for parallel queries. |
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