MoVR Load not working against 20.2.0

[vy-ton]

When running the following command using movr-load I'm getting the following error:

roachprod run $CLUSTER:10 <<EOF
    sudo docker run --rm cockroachdb/movr:20.07.1 --app-name "movr-load" --url "postgres://root@$CLUSTER-0010.roachprod.crdb.io:26257/movr?sslmode=disable" load --multi-region --num-users 100 --num-rides 100 --num-vehicles 10 --city "new york" --city "chicago" --city "seattle"
EOF

Error

```Status: Downloaded newer image for cockroachdb/movr:20.07.1
[INFO] (MainThread) connected to movr database @ postgres://[email protected]:26257/movr?sslmode=disable
[INFO] (MainThread) Loading multi region MovR
[INFO] (MainThread) initializing tables
[INFO] (MainThread) applying schema changes to make this database multi-region (this may take up to a minute).
[INFO] (MainThread) altering primary keys...
[INFO] (MainThread) altering foreign keys and dropping old indexes...
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1189, in _execute_context
    self.dialect.do_execute(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/default.py", line 509, in do_execute
    cursor.execute(statement, parameters)
psycopg2.errors.UndefinedObject: index "vehicles_auto_index_fk_owner_id_ref_users" does not exist


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "./loadmovr.py", line 574, in <module>
    run_data_loader(conn_string, cities= get_cities(args.city), num_users= args.num_users, num_rides= args.num_rides, num_vehicles= args.num_vehicles, num_histories= args.num_histories,
  File "./loadmovr.py", line 449, in run_data_loader
    with MovR(conn_string, init_tables=(not skip_reload_tables), multi_region = use_multi_region, echo=echo_sql) as movr:
  File "/usr/src/app/movr.py", line 29, in __init__
    self.run_multi_region_transformations()
  File "/usr/src/app/movr.py", line 249, in run_multi_region_transformations
    self.run_queries_in_separate_transactions(queries_to_run["fk_alters"])
  File "/usr/src/app/movr.py", line 184, in run_queries_in_separate_transactions
    run_transaction(sessionmaker(bind=self.engine),
  File "/usr/local/lib/python3.8/site-packages/cockroachdb/sqlalchemy/transaction.py", line 34, in run_transaction
    return _txn_retry_loop(session, callback, max_retries)
  File "/usr/local/lib/python3.8/site-packages/cockroachdb/sqlalchemy/transaction.py", line 79, in _txn_retry_loop
    ret = callback(conn)
  File "/usr/src/app/movr.py", line 185, in <lambda>
    lambda session: session.execute(query))
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", line 1175, in execute
    return self._connection_for_bind(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 948, in execute
    return meth(self, multiparams, params)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/sql/elements.py", line 269, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1055, in _execute_clauseelement
    ret = self._execute_context(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1195, in _execute_context
    self._handle_dbapi_exception(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1411, in _handle_dbapi_exception
    util.raise_from_cause(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/compat.py", line 265, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/compat.py", line 248, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1189, in _execute_context
    self.dialect.do_execute(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/engine/default.py", line 509, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (psycopg2.errors.UndefinedObject) index "vehicles_auto_index_fk_owner_id_ref_users" does not exist
 [SQL: 'DROP INDEX vehicles_auto_index_fk_owner_id_ref_users;'] (Background on this error at: http://sqlalche.me/e/f405)```

[blathers-crl]

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[rafiss]

Looks like the issue is that the altering foreign keys and dropping old indexes... is trying to drop the vehicles_auto_index_fk_owner_id_ref_users index, which doesn't exist. So we could probably fix this by using DROP INDEX IF EXISTS, if possible.

[rafiss]

fixed by cockroachdb/movr#104