Debug task: fix the idempotency problem (client's repeated request creates a duplicate operation) and the Outbox problem (two workers publish the same events)

To fix the idempotency issue and the Outbox problem, you need to:

1. Idempotency: ensure that repeated client requests do not create duplicate operations. This can be achieved by:

   • Using a unique operation identifier (e.g., request_id) that the client generates and sends with the request.
   • When processing the request, check if an operation with such request_id has already been completed, and if so — return the result without re-executing.

2. Outbox duplication issue occurs when multiple workers read and publish the same events simultaneously. Solutions:

   • Use a locking mechanism or mark the event status (e.g., "in processing") so that one worker handles the event.
   • Apply transactions and atomic operations when updating the event status.

Example in Python using a database and a unique request_id:

import sqlite3

conn = sqlite3.connect('example.db')
cursor = conn.cursor()

# Operations table
cursor.execute('''
CREATE TABLE IF NOT EXISTS operations (
    request_id TEXT PRIMARY KEY,
    result TEXT
)
''')
conn.commit()

def process_request(request_id, data):
    cursor.execute('SELECT result FROM operations WHERE request_id = ?', (request_id,))
    row = cursor.fetchone()
    if row:
        return row[0]  # Return the already processed result

    # Process the operation
    result = f"Processed {data}"

    # Save the result with request_id
    cursor.execute('INSERT INTO operations (request_id, result) VALUES (?, ?)', (request_id, result))
    conn.commit()

    return result

For Outbox, you can add a status field to events and update it atomically, so that one worker marks the event as "in processing" and prevents other workers from taking it.