db_user_namespace

db_user_namespace is the PostgreSQL setting that controls whether PostgreSQL enables per-database user names.

Note

Fact — official short description: “Enables per-database user names.”

Identity

Type , Valuebool: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueConnections and Authentication / Authentication: Upstream classification
Latest boot value , Valueoff: off

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–16
Removed in	PG17
Introduction commit	Not asserted: predates the PG9.0 research boundary
Commit date	—
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG9.0–16	`off`	—	off

How it works

db_user_namespace enables per-database user names. This legacy feature represented users internally as user@database and was removed in PostgreSQL 17; it is not a modern tenant-isolation mechanism.

db_user_namespace is a SIGHUP-context setting: a configuration reload activates the new server value without a restart; subsequent operations that consult it use the refreshed value.

The final authentication path combines this setting with pg_hba.conf, role attributes, credential material, client capabilities, and sometimes operating-system identity services.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Do not adopt or tune db_user_namespace: it was a legacy compatibility feature and is absent from PostgreSQL 17+. Migrate to ordinary cluster-wide roles with explicit authorization.
OLAP	Do not build analytical tenancy on db_user_namespace. Use roles, schemas, databases, and row-level security according to the required boundary.
Small nodes	Leave db_user_namespace off on old releases and remove dependencies before upgrading; it provides no useful small-node optimization.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG16; 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: PG9.0–16 unmodified; OLAP: PG9.0–16 unmodified; CRIT: PG9.0–16 unmodified; TINY: PG9.0–16 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Editing db_user_namespace without reloading configuration and verifying the effective value and subsequent behavior.
Changing one authentication setting without testing pg_hba.conf ordering, existing secrets, mappings, and every client library.
Weakening identity policy to solve connection churn or CPU cost that should be addressed with pooling and capacity planning.
Changing db_user_namespace globally without a rollback plan and a client or operational compatibility test.

password_encryption · scram_iterations · md5_password_warnings · authentication_timeout · oauth_validator_libraries · krb_server_keyfile