C24: Incomplete startup packet (client failed to connect)

Category: Connection Events
SQLSTATE: 08P01 (Class 08 - Connection Exception: protocol_violation)
Urgency: low

Example Postgres Log Output:

LOG: incomplete startup packet


This message occurs when PostgreSQL received a TCP connection, but the client didn't complete sending the remaining data to actually start establishing a Postgres connection.

Before PostgreSQL 12, where the behaviour was altered, this commonly occurred when third-party tools did health checks on a PostgreSQL database by doing a TCP connection and then immediately abandoning it again after the server acknowledges the connection on the TCP level.

You can reproduce this by running telnet localhost 5432 or nc -vz localhost 5432 which will result in this message being printed to the Postgres logs.

Starting with PostgreSQL 12 this message has been reduced to DEBUG1 level and should no longer be visible for production systems.

Recommended Action:

No action is necessary - this log message can be safely ignored.

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