ssl_groups

ssl_groups is the PostgreSQL setting that defines the group(s) to use for Diffie-Hellman key exchange.

Note

Fact — official short description: “Sets the group(s) to use for Diffie-Hellman key exchange.”

Identity

Type , Valuestring: 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 / SSL: Upstream classification
Latest boot value , ValueX25519:prime256v1: X25519:prime256v1

Lifecycle

Fact	Value
First observed	PG18
Present in	PG18–19 Beta 3
Removed in	No
Introduction commit	`3d1ef3a15c3e` — Support configuring multiple ECDH curves
Commit date	2024-10-24
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG18–19 Beta 3	`X25519:prime256v1`	—	X25519:prime256v1

How it works

ssl_groups sets the group(s) to use for Diffie-Hellman key exchange. Multiple groups can be specified using a colon-separated list. PostgreSQL 18 accepts an ordered colon-separated list, replacing the former single ssl_ecdh_curve choice and covering supported key-exchange groups.

ssl_groups 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. Existing TLS sessions are not renegotiated.

It participates in the TLS context used for new handshakes. ssl enables transport, pg_hba.conf decides which connection classes require it, and the certificate, key, CA, revocation, protocol, and cipher settings must form one valid policy.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Treat ssl_groups as transport-security policy rather than a performance knob. Follow the organization’s TLS baseline and test certificate rotation, reload, and every client class.
OLAP	Use the same TLS floor for analytical traffic; benchmark only after correctness because bulk transfer may expose CPU cost but is not a reason to accept obsolete protocols.
Small nodes	Keep ssl_groups simple and secure, using managed certificates and library defaults reviewed for the installed OpenSSL version. Rehearse renewal before expiry.

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: PG18–19 Beta 3 unmodified; OLAP: PG18–19 Beta 3 unmodified; CRIT: PG18–19 Beta 3 unmodified; TINY: PG18–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Editing ssl_groups without reloading configuration and verifying the effective value and subsequent behavior.
Updating only one TLS file or policy knob and leaving an invalid chain, unreadable key, or incompatible protocol set.
Assuming a reload renegotiates existing sessions; TLS policy changes affect new handshakes.
Changing ssl_groups globally without a rollback plan and a client or operational compatibility test.

ssl_ciphers · ssl_tls13_ciphers · ssl_min_protocol_version · ssl_max_protocol_version · ssl_prefer_server_ciphers