function can only be called when server is in binary upgrade mode

Symptoms

A statement failed with SQLSTATE 55P02 (cant_change_runtime_param), reported at severity ERROR. This is a Object Not In Prerequisite State condition: PostgreSQL emits the message function can only be called when server is in binary upgrade mode.

• The client receives SQLSTATE 55P02 (cant change runtime param).
• The operation is rejected at ERROR level; the statement does not complete.

What the server log shows

ERROR:  function can only be called when server is in binary upgrade mode

Why PostgreSQL raises this

Class 55 (Object Not In Prerequisite State) is raised when an object exists but is not in a state that allows the requested operation right now.

As described in PostgreSQL’s Appendix A PostgreSQL Error Codes, SQLSTATE 55P02 carries the condition name cant_change_runtime_param in class Object Not In Prerequisite State. (Paraphrased — see the linked reference for the exact wording.)

Common causes

• The object is locked, in use, or being modified by another session.
• A required precondition (e.g. an index, a prepared state) is not met.
• The operation cannot run while the object is in its current state.

How to fix it

1. Wait for the conflicting session/operation to finish, then retry.
2. Establish the missing precondition before retrying.
3. Check for blocking locks with pg_locks.

Version applicability

This message is present in PostgreSQL 15, 16, 17, 18 and 19.

Related & next steps

• SQLSTATE 55P02 — Cant Change Runtime Param (full reference)
• PostgreSQL error code index

Reference: PostgreSQL Appendix A PostgreSQL Error Codes.