Flask-Migrate hangs on table modificiation

Question

I have an issue on running the upgrade command with Flask-Migrate. Originally I was trying to modify three tables at once and it hung, I narrowed it down to a specific table (the other upgrades worked without issue). I don't see any locks on the database. I'm using Postgres and just working in a development environment at the moment. The migrate command seems to work fine and generates the upgrade method without any issues (see code)

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.drop_column('equipment', 'criteria_notes')
    # ### end Alembic commands ###

Once I run the upgrade command I get stuck here:

>flask db upgrade
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade 76bf72d8e0e4 -> 1723c01f0606, empty message

with a blinking cursor. When I exit out of the command window (I'm using windows) no changes have been applied.

I've tried

• Restarting computer
• Looking for locks or other sessions with pgAdmin
• Modifying other tables, was able to add and drop columns

Answer 1

You likely have other processes connected to this DB.

This happened to me, I had celery, uwsgi, and a separate custom process all connected to the flask DB on a production server, and I was wonder why the upgrades were hanging.

Once I shut these processes down manually the upgrade script ran fine without hanging.

In my case I also tried rebooting before realizing this, and this did not help because these other processes were programmed to startup on boot.