allow_in_place_tablespaces

allow_in_place_tablespaces — Allows tablespaces directly inside pg_tblspc, for testing. Observed in PG10–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with superuser context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Allows tablespaces directly inside pg_tblspc, for testing.”

Identity

Type , Valuebool: Upstream pg_settings type
Context , Valuesuperuser: Settable at runtime by a superuser
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueDeveloper Options: Upstream classification
Latest boot value , Valueoff: off

Lifecycle

Fact	Value
First observed	PG10
Present in	PG10–19 Beta 3
Removed in	No
Introduction commit	`7bdbbb87340f` — Allow “in place” tablespaces.
Commit date	2022-07-27
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG10–19 Beta 3	`off`	—	off

How it works

allow_in_place_tablespaces lets a superuser create a tablespace with an empty location directly under pg_tblspc instead of using the normal external-location symbolic link. It exists to test primary and standby instances on one machine.

The directory layout violates assumptions made by backup and tablespace-management tools, which normally expect pg_tblspc entries to be links. It does not make colocated tablespaces independent storage.

The switch is consulted for the privileged CREATE TABLESPACE operation and is not a performance setting. Objects created this way can remain after the setting is turned off. Its superuser context permits an authorized session change without a server restart.

Tuning advice

Tip

Advice. These are workload-specific starting points and must be validated with measurements.

Workload	Guidance
OLTP	Do not tune production OLTP with allow_in_place_tablespaces. Enable it only for a bounded reproduction with an owner, log/disk budget, rollback condition, and evidence-capture plan; restore the default immediately afterward.
OLAP	Long analytical runs can amplify allow_in_place_tablespaces’s debug overhead and artifacts. Prefer standard EXPLAIN and statistics first, and isolate any developer experiment from normal users.
Small nodes	Keep allow_in_place_tablespaces at its upstream default. A small host has less spare CPU, disk, connection, and log capacity for developer instrumentation.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

Template	Effective value	Versus upstream boot	Source expression
OLTP	Unmodified	—	—
OLAP	Unmodified	—	—
CRIT	Unmodified	—	—
TINY	Unmodified	—	—

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG10–19 Beta 3 unmodified; OLAP: PG10–19 Beta 3 unmodified; CRIT: PG10–19 Beta 3 unmodified; TINY: PG10–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Leaving allow_in_place_tablespaces enabled after the bounded diagnostic or recovery task.
Running the experiment on the only copy of production data.
Underestimating log, core-file, temporary-file, WAL, CPU, or connection-slot amplification.
Treating a server that merely starts or completes a query as proof that data and behavior are correct.

data_directory · wal_level · hot_standby · archive_mode