Wiki / Configuration Parameters

This allows sequential scans of large tables to synchronize with each other, so that concurrent scans read the same block at about the same time and hence share the I/O workload. When this is enabled, a scan might start in the middle of the table and then “wrap around” the end to cover all rows, so as to synchronize with the activity of scans already in progress. This can result in unpredictable changes in the row ordering returned by queries that have no ORDER BY clause. Setting this parameter to off ensures the pre-8.3 behavior in which a sequential scan always starts from the beginning of the table. The default is on.

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

boot val

on

category

Version and Platform Compatibility / Previous PostgreSQL Versions

context

user

documented

true

enumvals

Unknown

extra desc

Unknown

lang

en

max val

Unknown

metadata version

18

min val

Unknown

name

synchronize_seqscans

short desc

Enables synchronized sequential scans.

source

pg-settings-source-snapshot

unit

Unknown

vartype

bool