DateStyle

DateStyle is the PostgreSQL setting that defines the display format for date and time values.

Note

Fact — official short description: “Sets the display format for date and time values.”

Identity

Type , Valuestring: Upstream pg_settings type
Context , Valueuser: Settable by an ordinary user
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueClient Connection Defaults / Locale and Formatting: Upstream classification
Latest boot value , ValueISO, MDY: ISO, MDY

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–19 Beta 3
Removed in	No
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
PG9.0–19 Beta 3	`ISO, MDY`	—	ISO, MDY

How it works

DateStyle sets the display format for date and time values. Also controls interpretation of ambiguous date inputs. The value has two independent parts: an output style and a DMY/MDY/YMD field order; the latter also resolves ambiguous input.

DateStyle is a USER-context setting. An authorized role can change it for a session, while ALTER ROLE or ALTER DATABASE can establish a default for future sessions.

It changes representation, parsing, or locale behavior at the client boundary rather than physical storage. Coordinate it with the other locale and formatting settings and with driver-native binary or typed protocols.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Treat DateStyle as an application contract, not a performance knob. Standardize it per role or connection pool and keep wire formats explicit where clients parse text.
OLAP	Pin DateStyle for export, reporting, and reproducible analytical jobs; prefer explicit SQL formatting when a file or API has a durable schema.
Small nodes	Keep the upstream or locale-derived value unless a client requires another one. A smaller server gains no capacity from changing DateStyle.

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: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Changing DateStyle in one session and assuming role defaults, database defaults, or other pooled sessions changed with it.
Assuming a presentation setting changes stored values or server-side type semantics.
Changing a role or database default without testing text-parsing clients, exports, and pooled sessions.
Parsing an ambiguous value such as 01/02/03 under an unexpected MDY/DMY order.

IntervalStyle · TimeZone · lc_time · timezone_abbreviations · log_timezone