How to diagnose and fix the 39P03 event_trigger_protocol_violated error code in Postgres.

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The 39P03 error code in PostgreSQL, known as event_trigger_protocol_violated, indicates that there has been a protocol violation with an event trigger. This error typically occurs when an event trigger function does not follow the correct protocol for executing commands or accessing data. To diagnose and fix this error, consider the following steps:

  1. Understand Event Trigger Functions: Event triggers are special kinds of triggers that are fired for certain database events such as DDL statements (e.g., CREATE, ALTER, DROP). Unlike regular triggers, event triggers do not operate on rows or tables but on the database events themselves.
  2. Review the Event Trigger Function: Check the code of your event trigger function to ensure it follows the correct protocol. For example, an event trigger function should not attempt to execute queries that modify the database since event triggers are intended for monitoring purposes.
  3. Check for Disallowed Commands: Ensure that your event trigger function does not contain any commands that are disallowed in the context of an event trigger. For instance, an event trigger function should not include data-modifying commands.
  4. Consult PostgreSQL Documentation: Review the PostgreSQL documentation regarding event triggers to understand the restrictions and correct usage patterns for event trigger functions.

Here are some examples and sample code to illustrate potential scenarios:

  • Scenario 1: Event trigger function attempts to modify data.
  CREATE FUNCTION disallowed_event_trigger_function()
  RETURNS event_trigger AS $$
  BEGIN
    -- This is not allowed in an event trigger function
    INSERT INTO audit_table VALUES ('A DDL command was executed');
  END;
  $$ LANGUAGE plpgsql;

  CREATE EVENT TRIGGER disallowed_event_trigger
  ON ddl_command_end
  EXECUTE FUNCTION disallowed_event_trigger_function();

To fix this, remove any data-modifying commands from the event trigger function.

  • Scenario 2: Event trigger function using disallowed commands.
  CREATE FUNCTION another_disallowed_event_trigger_function()
  RETURNS event_trigger AS $$
  BEGIN
    -- This is not allowed in an event trigger function
    DROP TABLE some_table;
  END;
  $$ LANGUAGE plpgsql;

  CREATE EVENT TRIGGER another_disallowed_event_trigger
  ON ddl_command_end
  EXECUTE FUNCTION another_disallowed_event_trigger_function();

To fix this, ensure that the event trigger function does not contain any DDL commands or other disallowed operations.

Remember, when diagnosing and fixing the 39P03 error code, it’s crucial to ensure that the event trigger function adheres to the protocol defined by PostgreSQL for event triggers. This means avoiding any commands that could modify the database state within the event trigger function. If the problem persists after reviewing and correcting the function, consulting the official PostgreSQL documentation or seeking help from the PostgreSQL community can be beneficial for additional troubleshooting.

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