allow_in_place_tablespaces — PostgreSQL configuration parameter

Allows tablespaces to be created as directories inside pg_tblspc, when an empty location string is provided to the CREATE TABLESPACE command.

At a glance

What it does

Allows tablespaces to be created as directories inside pg_tblspc, when an empty location string is provided to the CREATE TABLESPACE command. This is intended to allow testing replication scenarios where primary and standby servers are running on the same machine. Such directories are likely to confuse backup tools that expect to find only symbolic links in that location. Only superusers and users with the appropriate SET privilege can change this setting.

(Description quoted from the official PostgreSQL documentation.)

How to apply a change

Can be set per session with SET, per role/database with ALTER ROLE/DATABASE ... SET, or globally in postgresql.conf.

Inspect the current value and source with SHOW allow_in_place_tablespaces; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'allow_in_place_tablespaces';.

Tuning guidance

This is a developer and debugging aid, not a performance knob. Leave it at the default in production; enable it only temporarily, on a non-production or carefully controlled system, while diagnosing a specific problem. Several options in this group add overhead, generate large volumes of log output, or can damage data if misused — turn them off again as soon as the investigation is done.

Reference

PostgreSQL documentation — allow_in_place_tablespaces.