Hi! So, I have a traditional Flask app using flask-sqlalchemy and
sqlalchemy ORM, served with uwsgi. Uwsgi is set with processes=4 and
threads=4. Yesterday I added grequests to improve a single area of the app
a bit (I had to do a couple hundred external API calls to build a single
data structure). No problem- except that I started getting errors like
/usr/local/lib/python2.7/dist-packages/flask_sqlalchemy/__init__.py", line
423, in first_or_404 rv = self.first() File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line
2634, in first ret = list(self[0:1]) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line
2457, in __getitem__ return list(res) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line
2736, in __iter__ return self._execute_and_instances(context) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line
2751, in _execute_and_instances result =
conn.execute(querycontext.statement, self._params) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line
914, in execute return meth(self, multiparams, params) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/sql/elements.py", line
323, in _execute_on_connection return
connection._execute_clauseelement(self, multiparams, params) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line
1010, in _execute_clauseelement compiled_sql, distilled_params File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line
1078, in _execute_context None, None) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line
1341, in _handle_dbapi_exception exc_info File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/compat.py", line
200, in raise_from_cause reraise(type(exception), exception, tb=exc_tb,
cause=cause) File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line
1073, in _execute_context context = constructor(dialect, self, conn, *args)
File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py",
line 558, in _init_compiled self.cursor = self.create_cursor() File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line
748, in create_cursor return self._dbapi_connection.cursor() File
"/usr/local/lib/python2.7/dist-packages/sqlalchemy/pool.py", line 852, in
cursor return self.connection.cursor(*args, **kwargs) File
"/usr/local/lib/python2.7/dist-packages/mysql/connector/connection.py",
line 807, in cursor raise errors.OperationalError("MySQL Connection not
available.") OperationalError: (mysql.connector.errors.OperationalError)
MySQL Connection not available.
>From playing around with it, importing grequests was the line of code that
made the error appear/dis-appear. Further experimenting shows that `import
gevent.monkey; gevent.monkey.patch_all()` anywhere in the code breaks the
app as well. This doesn't happen on every request, and I am not actually
using greenlets or the gevent loop anywhere in the endpoints I am
accessing. For now this is easy enough for me to just rip out grequests,
but I was wondering if anyone had any ideas as to why this is happening?
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