trace_connection_negotiation

trace_connection_negotiation — Logs details of pre-authentication connection handshake. Observed in PG17–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with postmaster context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Logs details of pre-authentication connection handshake.”

Identity

Type , Valuebool: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
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	PG17
Present in	PG17–19 Beta 3
Removed in	No
Introduction commit	`705843d294d5` — Enhance libpq encryption negotiation tests with new GUC
Commit date	2024-04-08
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG17–19 Beta 3	`off`	—	off

How it works

trace_connection_negotiation logs details from the pre-authentication connection negotiation path, providing evidence for protocol, encryption, and handshake debugging before normal authentication logs are available.

It is a server-start setting, so enabling it affects subsequent connection handshakes cluster-wide until restart. It does not alter authentication rules or make negotiation succeed.

Handshake logs can be high-volume and reveal network or client capability details. Use a controlled reproduction and protect the resulting server logs. Its postmaster context fixes the value at server start; changing it requires a 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 trace_connection_negotiation. 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 trace_connection_negotiation’s debug overhead and artifacts. Prefer standard EXPLAIN and statistics first, and isolate any developer experiment from normal users.
Small nodes	Keep trace_connection_negotiation 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: PG17–19 Beta 3 unmodified; OLAP: PG17–19 Beta 3 unmodified; CRIT: PG17–19 Beta 3 unmodified; TINY: PG17–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Leaving trace_connection_negotiation 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.

log_connections · authentication_timeout · ssl · pre_auth_delay · log_error_verbosity