EC
08006
PostgreSQLERRORNotableConnection ExceptionMEDIUM confidence

connection failure

What this means

An established connection to the Postgres server was lost unexpectedly during a session. The error is raised on the client side when the network socket is closed or reset before the server finished sending a response.

Why it happens
  1. 1Network interruption between client and server (firewall rule, NAT timeout, VPC issue)
  2. 2Postgres server process (postmaster or backend) crashed or was killed by the OOM killer
  3. 3Server-side idle_in_transaction_session_timeout or statement_timeout terminated the backend
  4. 4Connection pool proxy (pgBouncer, RDS Proxy) closed an idle connection
  5. 5SSL renegotiation failure or certificate mismatch
How to reproduce

A long-running query is interrupted by a network drop or server-side timeout.

trigger — this will error
trigger — this will error
-- Simulate by terminating the backend from another session:
SELECT pg_terminate_backend(pg_backend_pid());
-- The victim session receives 08006

expected output

FATAL:  terminating connection due to administrator command
server closed the connection unexpectedly
This probably means the server terminated abnormally before or while processing the request.

Fix 1

Implement connection retry with exponential backoff

WHEN When transient network issues are the cause and the operation is idempotent.

Implement connection retry with exponential backoff
-- Liveness probe before executing:
SELECT 1;

-- Reconnect and retry in application code on SQLSTATE 08006.
-- Use connection pool max_retries and reconnect_on_failure settings.

Why this works

Postgres backend processes are independent OS processes. When a backend crashes or the network drops, the client socket receives EOF or RST. The client driver raises 08006. Reconnecting creates a fresh backend process via the postmaster fork pathway.

Fix 2

Tune keepalive and timeout settings

WHEN When idle connections are being dropped by NAT/firewalls or proxy timeouts.

Tune keepalive and timeout settings
-- Set server-side idle timeout (Postgres 9.6+):
ALTER SYSTEM SET idle_in_transaction_session_timeout = '5min';
SELECT pg_reload_conf();

-- Connection string keepalive params:
-- keepalives=1&keepalives_idle=60&keepalives_interval=10&keepalives_count=5

Why this works

TCP keepalive probes prevent NAT tables and firewalls from expiring idle connections. idle_in_transaction_session_timeout terminates backends stuck in a transaction, freeing locks; the client receives 08006 and knows to reconnect.

What not to do

✕ Disable SSL to work around SSL-related 08006 errors

Exposes credentials and data in transit to eavesdropping; fix the certificate issue instead.

Version notes
Postgres 9.6+

idle_in_transaction_session_timeout parameter added; previously only statement_timeout was available.

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