I'm looking to potentially use background task(s) to offload sending of emails and updating of other offline resources, and I'm trying to sort out what the implications are.
In the PDF of the book (just released for free, thank you!), page 389, section 8.5 "Sending messages using a background task" is the following text: "Also notice that it is important to commit any change as soon as possible in order not to lock the database to other concurrent processes. As noted in Chapter 4, this type of background process should not be executed via cron (except perhaps for cron @reboot) because you need to be sure that no more than one instance is running at the same time." So I'm puzzled, if the database is locked, then shouldn't multiple accessors should be fine? The email task example, spanning pages 388-389, does a db.commit() every in body of a loop that is processing the rows rather than at the end of the loop. What/where are the locks obtained in this sample script? Since the script never exits, it can't be just running the script? Is the lock obtained on the update call and then released on the commit? I'm not having much luck figuring out how to avoid locking issues when I can't seem to figure out when Web2py takes and releases locks. I've just re-read chapter 6 and am still puzzled. Pointers to where else to look are appreciated. Thanks -Doug
