[Django]-Best approach to handle concurrency in Django for eauction toy-app

Have you checked out Celery? You might process your queries asynchronously, queuing the queries and then handing results or errors back when they’re available. That seems like a likely path to take if you want to avoid locking.

Otherwise, it does seem like some locking would need to occur.

Would it be possible for you to add a highest_bid column to Products. If my logic is not off, you could then update the highest bid where product_id = x and highest < current_bid. If this query indicates that a row has been updated then you add the new record to the bid table. This would probably mean that you would have to have a default value for highest_bid column.