time banking, alternative currencies

Hey django! This is slightly off-topic, sorry. My 2nd option isn't, so I try here. I was asked by a friend how to create a platform where therapists can exchange goods&services. My first idea was to plug into an existing time banking / time dollar / minuto service, and let them handle the

Lock Django DB on 9 of 10 concurrent uwsgi workers - how to?

What is the most elegant way to lock the Django DB while I make a complex transaction (read, decide, write) ... during which no other uwsgi worker should have access (or at least no write access) to that table? I am using Django + db.sqlite3 + uwsgi (+ nginx). Thanks a lot! Andreas