Airflow "Something Bad Has Happened" Error: Session Table does not exist - postgresql

Question

I'm trying to crteate a simple test dag to write a test query in a AWS EC2 postgres instance behind a bastion host.
After adding this script in airflow with touch pg_test.py and nano pg_test.py
from airflow import DAG
from airflow.operators.postgres_operator import PostgresOperator
from datetime import datetime
Query = """DROP TABLE IF EXISTS dataset.test;
create TABLE dataset.test as (select * from table
);"""
dag = DAG(
'postgres_test_dag',
schedule_interval = '0 * * * *',
start_date = datetime(2021, 3, 20), catchup = False
)
create_table = PostgresOperator(
task_id='create_table',
dag=dag,
postgres_conn_id='postgres_dwh',
sql=Query
)
create_table
and installing the airflow postgres provider with
`pip install apache-airflow-providers-postgres`
I'm getting this error and I do not know how to solve it
Something bad has happened.
Airflow is used by many users, and it is very likely that others had similar problems and you can easily find
a solution to your problem.
Consider following these steps:
* gather the relevant information (detailed logs with errors, reproduction steps, details of your deployment)
* find similar issues using:
* GitHub Discussions
* GitHub Issues
* Stack Overflow
* the usual search engine you use on a daily basis
* if you run Airflow on a Managed Service, consider opening an issue using the service support channels
* if you tried and have difficulty with diagnosing and fixing the problem yourself, consider creating a bug report.
Make sure however, to include all relevant details and results of your investigation so far.
Python version: 3.8.10
Airflow version: 2.2.4
Node: ip-XXXXXXXXX.ec2.internal
-------------------------------------------------------------------------------
Traceback (most recent call last):
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1276, in _execute_context
self.dialect.do_execute(
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/default.py", line 608, in do_execute
cursor.execute(statement, parameters)
psycopg2.errors.UndefinedTable: relation "session" does not exist
LINE 2: FROM session
^
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/airflow/.local/lib/python3.8/site-packages/flask/app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "/home/airflow/.local/lib/python3.8/site-packages/flask/app.py", line 1953, in full_dispatch_request
return self.finalize_request(rv)
File "/home/airflow/.local/lib/python3.8/site-packages/flask/app.py", line 1970, in finalize_request
response = self.process_response(response)
File "/home/airflow/.local/lib/python3.8/site-packages/flask/app.py", line 2269, in process_response
self.session_interface.save_session(self, ctx.session, response)
File "/home/airflow/.local/lib/python3.8/site-packages/airflow/www/session.py", line 32, in save_session
return super().save_session(*args, **kwargs)
File "/usr/local/lib/python3.8/dist-packages/flask_session/sessions.py", line 553, in save_session
saved_session = self.sql_session_model.query.filter_by(
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/orm/query.py", line 3429, in first
ret = list(self[0:1])
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/orm/query.py", line 3203, in __getitem__
return list(res)
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/orm/query.py", line 3535, in __iter__
return self._execute_and_instances(context)
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/orm/query.py", line 3560, in _execute_and_instances
result = conn.execute(querycontext.statement, self._params)
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1011, in execute
return meth(self, multiparams, params)
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/sql/elements.py", line 298, in _execute_on_connection
return connection._execute_clauseelement(self, multiparams, params)
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1124, in _execute_clauseelement
ret = self._execute_context(
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1316, in _execute_context
self._handle_dbapi_exception(
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1510, in _handle_dbapi_exception
util.raise_(
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/util/compat.py", line 182, in raise_
raise exception
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1276, in _execute_context
self.dialect.do_execute(
File "/home/airflow/.local/lib/python3.8/site-packages/sqlalchemy/engine/default.py", line 608, in do_execute
cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (psycopg2.errors.UndefinedTable) relation "session" does not exist
LINE 2: FROM session
^
[SQL: SELECT session.id AS session_id_1, session.session_id AS session_session_id, session.data AS session_data, session.expiry AS session_expiry
FROM session
WHERE session.session_id = %(session_id_1)s
LIMIT %(param_1)s]
[parameters: {'session_id_1': '3c0eb88d-9042-4951-94a1-c6d127d02450', 'param_1': 1}]
(Background on this error at: http://sqlalche.me/e/13/f405)
I already tried to reboot the airflow instance and reconnect to the terminal but did not work. I suspect that it has something to with the connection to postgres (AWS EC2) and the internal airflow postgres database.
Do you have any suggestions ? And maybe also a precise explanation of this issue? It would be very appreciated.

Answer 1

The problem is that Airflow is looking for a session table in the metadata database but isn't finding one. I see in the migration that this table was added fairly recently, you can run airflow db upgrade to run the latest migrations and that should fix your problem.