select *from pg_settings pswhere 1=1and ps.name in ('force_parallel_mode','max_worker_processes','max_parallel_workers','max_parallel_maintenance_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','parallel_leader_participation'
)
;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_maintenance_workers | 4 | | Resource Usage / Asynchronous Behavior | Sets the maximum number of parallel processes per maintenance operation. | | user | integer | session | 0 | 1024 | | 2 | 2 | | | fmax_parallel_workers | 8 | | Resource Usage / Asynchronous Behavior | Sets the maximum number of parallel workers that 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_leader_participation | on | | Resource Usage / Asynchronous Behavior | Controls whether Gather and Gather Merge also run subplans. | Should gather nodes also run subplans, or just gather tuples? | user | bool | default | | | | on | on | | | 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
(10 rows)
Allows the leader process to execute the query plan under Gather and Gather Merge nodes instead of waiting for worker processes.
The default is on.
Setting this value to off reduces the likelihood that workers will become blocked because the leader is not reading tuples fast enough,
but requires the leader process to wait for worker processes to start up before the first tuples can be produced.
The degree to which the leader can help or hinder performance depends on the plan type, number of workers and query duration.
