default_toast_compression

default_toast_compression is the PostgreSQL setting that defines the default compression method for compressible values.

Note

Fact — official short description: “Sets the default compression method for compressible values.”

Identity

Type , Valueenum: 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 , Valuepglz, lz4: — for non-enum types
Category , ValueClient Connection Defaults / Statement Behavior: Upstream classification
Latest boot value , Valuelz4: lz4

Lifecycle

Fact	Value
First observed	PG14
Present in	PG14–19 Beta 3
Removed in	No
Introduction commit	`bbe0a81db69b` — Allow configurable LZ4 TOAST compression.
Commit date	2021-03-19
Discussion	thread 1 · thread 2

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG14–18	`pglz`	—	pglz
PG19 Beta 3	`lz4`	—	lz4

How it works

default_toast_compression sets the default compression method for compressible values. It chooses pglz or, when compiled in, lz4 for newly written compressible values; a column COMPRESSION clause overrides the session default.

default_toast_compression 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 supplies a default only when SQL omits an explicit choice, so schema migrations, object-level options, privileges, and later ALTER operations can override or outlive it.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Benchmark pglz versus lz4 with representative wide values, update rates, CPU, WAL, and storage. Prefer explicit column COMPRESSION for important schemas over a surprising session default.
OLAP	LZ4 can favor faster compression and decompression when the build supports it, but measure actual compressibility and scan behavior before changing new-write policy.
Small nodes	Keep pglz unless CPU-versus-space measurements and package support justify lz4; changing the default does not recompress existing values.

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: PG14–19 Beta 3 unmodified; OLAP: PG14–19 Beta 3 unmodified; CRIT: PG14–19 Beta 3 unmodified; TINY: PG14–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Changing default_toast_compression in one session and assuming role defaults, database defaults, or other pooled sessions changed with it.
Expecting a changed default to rewrite existing objects or override explicit DDL clauses.
Ignoring tablespace privileges, installed access methods or compression support, and restore portability.
Changing default_toast_compression globally without a rollback plan and a client or operational compatibility test.

default_table_access_method · default_tablespace · temp_tablespaces · check_function_bodies · maintenance_work_mem