select *from pg_settings pswhere 1=1and ps.name in ('force_parallel_mode','max_worker_processes','max_parallel_workers','max_parallel_workers_per_gather','min_parallel_relation_size',-- add 9.6,remove from 10'min_parallel_index_scan_size','min_parallel_table_scan_size','parallel_tuple_cost','parallel_setup_cost');
name | setting | unit | category | short_desc | extra_desc | context | vartype | source | min_val | max_val | enumvals | boot_val | reset_val | sourcefile | sourceline | pending_restart
---------------------------------+---------+------+----------------------------------------+----------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+------------+---------+---------+---------+--------------+------------------+----------+-----------+------------+------------+-----------------force_parallel_mode | off | | Query Tuning / Other Planner Options | Forces use of parallel query facilities. | If possible, run query using a parallel worker and with parallel restrictions. | user | enum | default | | | {off,on,regress} | off | off | | | fmax_parallel_workers | 8 | | Resource Usage / Asynchronous Behavior | Sets the maximum number of parallel workers than can be active at one time. | | user | integer | default | 0 | 1024 | | 8 | 8 | | | fmax_parallel_workers_per_gather | 2 | | Resource Usage / Asynchronous Behavior | Sets the maximum number of parallel processes per executor node. | | user | integer | default | 0 | 1024 | | 2 | 2 | | | fmax_worker_processes | 8 | | Resource Usage / Asynchronous Behavior | Maximum number of concurrent worker processes. | | postmaster | integer | default | 0 | 262143 | | 8 | 8 | | | fmin_parallel_index_scan_size | 64 | 8kB | Query Tuning / Planner Cost Constants | Sets the minimum amount of index data for a parallel scan. | If the planner estimates that it will read a number of index pages too small to reach this limit, a parallel scan will not be considered. | user | integer | default | 0 | 715827882 | | 64 | 64 | | | fmin_parallel_table_scan_size | 1024 | 8kB | Query Tuning / Planner Cost Constants | Sets the minimum amount of table data for a parallel scan. | If the planner estimates that it will read a number of table pages too small to reach this limit, a parallel scan will not be considered. | user | integer | default | 0 | 715827882 | | 1024 | 1024 | | | fparallel_setup_cost | 1000 | | Query Tuning / Planner Cost Constants | Sets the planner's estimate of the cost of starting up worker processes for parallel query. | | user | real | default | 0 | 1.79769e+308 | | 1000 | 1000 | | | fparallel_tuple_cost | 0.1 | | Query Tuning / Planner Cost Constants | Sets the planner's estimate of the cost of passing each tuple (row) from worker to master backend. | | user | real | default | 0 | 1.79769e+308 | | 0.1 | 0.1 | | | f
(8 rows)
set max_parallel_workers_per_gather =0;explain
select count(1)
from tmp_t0
where 1=1
;Aggregate (cost=267858.75..267858.76 rows=1 width=8)-> Seq Scan on tmp_t0 (cost=0.00..242858.60 rows=10000060 width=0)
session 級別的并行控制
set max_parallel_workers=4; set max_parallel_workers_per_gather =4; set parallel_setup_cost =0; set parallel_tuple_cost =0; alter table test set (parallel_workers =4);
