SQLAlchemy Session.commit() hangs

Question

I am using scoped_sessions from SQLAlchemy (to MySQL) and running the SQL commit inside tornado's threadpool. In my unit test, the first time Session.commit() passes but the second Session.commit() hangs. I am closing the session properly after the first time commit. I enabled SQLAlchemy logging and I can see that there is nothing emitted after INSERT INTO ... for the second commit.

Answer 1

Having same issue (hang in later commit) brought me to this question earlier today. I've managed to resolve the issue by making sure that only one session is in place.

In my case I'm running integration tests with session test for each test and doing roll back in tear-down as described in docs. I've got all DB stuff wrapped in DatabaseService class which is responsible for the test setup (a derived TestDatabaseClass doing the session setup in ctor).

The problem was that I managed to initialize the DatabaseService instance (with test setup) twice and experienced the hang in the later created nested session's commit (or in explicit flush call). So making sure that only one DatabaseService exists and all DB queries goes thru one session did resolve the problem for me.