Configuration (enable_*) parameter related to execution plan in PG

ENABLE_* Parameters

stay pg in , Some with “ENABLE_*” Parameters at the beginning , These parameters provide methods that affect the query optimizer's choice of different execution plans .

If the execution plan chosen by the optimizer for a particular query is not optimal , These parameters can be set to force the optimizer to choose a better execution plan to solve this problem in the near future ,

But generally not in pg Change the default values of these parameter values in .

enable_seqscan:boolean

Whether to select full table scanning . In fact, full table scanning cannot be completely disabled , But turning this variable off will give the optimizer priority over other methods when they exist

enable_indexscan:boolean

Whether to select index scan

enable_bitmapscan:boolean

Whether to select bitmap scanning

enable_tidscan:boolean

Whether to select bitmap scanning

enable_nestloop:boolean

When multiple meters are connected , Whether to select nested loop connection . If set to “off”, The execution plan can only be connected by nested loops , The optimizer can only choose this path ,

But if there are other ways to connect , The optimizer will give preference to other methods .

enable_hashjoin:boolean

When multiple meters are connected , Whether to choose hash Connect

enable_mergejoin:boolean

When multiple meters are connected , Whether to choose merge Connect

enable_hashagg:boolean

Whether to use hash polymerization

enable_sort:boolean

Use explicit sort , If set to “off”, When there is only one way to sort the execution plan , The optimizer can only choose this path ,

But if there are other ways to connect , The optimizer will give preference to other methods .

Complete example ：http://github.crmeb.net/u/defu

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