Wiki / Configuration Parameters

Sets the planner's assumption about the effective size of the disk cache that is available to a single query. This is factored into estimates of the cost of using an index; a higher value makes it more likely index scans will be used, a lower value makes it more likely sequential scans will be used. When setting this parameter you should consider both PostgreSQL's shared buffers and the portion of the kernel's disk cache that will be used for PostgreSQL data files, though some data might exist in both places. Also, take into account the expected number of concurrent queries on different tables, since they will have to share the available space. This parameter has no effect on the size of shared memory allocated by PostgreSQL, nor does it reserve kernel disk cache; it is used only for estimation purposes. The system also does not assume data remains in the disk cache between queries. If this value is specified without units, it is taken as blocks, that is BLCKSZ bytes, typically 8kB. The default is 4 gigabytes (4GB). (If BLCKSZ is not 8kB, the default value scales proportionally to it.)

English manual coverage begins with PostgreSQL 7.4. Source history and runtime observations have their own recorded version boundaries.

boot val

524288

category

Query Tuning / Planner Cost Constants

context

user

documented

true

enumvals

Unknown

extra desc

That is, the total size of the caches (kernel cache and shared buffers) used for PostgreSQL data files. This is measured in disk pages, which are normally 8 kB each.

lang

en

max val

2147483647

metadata version

18

min val

1

name

effective_cache_size

short desc

Sets the planner's assumption about the total size of the data caches.

source

pg-settings-source-snapshot

unit

8kB

vartype

integer