No problem at all. The bit of magic that I forgot to tell explicitely is that db.commit() commits every opened transaction and starts a new one :D
just to be precise: "locking" is true currently only for sqlite engine, and that's because how sqlite works (it's like that also outside web2py world). SQLite blocks any attemp to write/read the db if there is one process writing to it. Note, if your site does mostly reading, than SQLite is fine with that. Additional note, if you're not using SQLite there are no "locks" at all. Mysql, mssql, postgres, etc can "support" many opened transactions..... Take it like that. Transactions are a way to provide consistent data to every reader/writer connected to a database. When you start a transaction you make sure that the changes you are making in that transaction get "seen" by others only when you commit it. When you are making updates/deletes "inside" a transaction, no-one will see those changes..... It's like cooking: you start with all the ingredients but you want to serve it when it's finished and cooked, and you don't want others to peek while mixing ingredients and putting it into the oven. Before the commit, everyone will just see ingredients; after commit, everyone will see the cooked "version". Again with the metaphore, with all the dbs a lot of people can concurrently see the ingredients (also when you started mixing and cooking) with no locks whatsoever. They just see the "version" the database saved with the last commit. SQLite instead "refuses" to provide that feature (currently there is a way, but it's far from this discussion) and allows no-one to access the ingredients if someone is mixing/cooking them. So, if there is only one daemon running, it's safe to commit every 500 or every 1 with all the dbs: if you commit every row everytime you app will try to see the queue will see a "freshier" version of it, if you commit every 500 the app will see a "older" version of the queue. The caveat of locking is valid for sqlite only: if you commit every 500 the app won't be allowed to read or write to the db while processing 1 to 500. If you commit every 1, the app will "lock" less.
