<p>I am having a postgres production database in production (which contains a lot of Data). now I need to modify the model of the tg-app to add couple of new tables to the database. </p>

<p>How do i do this? I am using sqlAlchemy.</p>

If you are just adding tables, and not modifying any of the tables which have the existing data in it, you can simply add the new sqlAlchemy table definitions to model.py, and run:
```
```
tg-admin sql create
```
```
This will not overwrite any of your existing tables.
For schema migration, you might take a look at
http://code.google.com/p/sqlalchemy-migrate/
although I haven't used it yet myself.
Always take a backup of the production database before migration activity.