python - SQLAlchemy query occassionally throws StatementError -

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i have flask application uses sqlalchemy connected mysql db running on production server (ubuntu machine).

75% of times issue post request application raises statementerror following stacktrace.

  [2015-06-18 17:25:46,512] {/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/flask/app.py:1423} error - exception on /conjugate/conjugate [post] traceback (most recent call last):   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app     response = self.full_dispatch_request()   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request     rv = self.handle_user_exception(e)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception     reraise(exc_type, exc_value, tb)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request     rv = self.dispatch_request()   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request     return self.view_functions[rule.endpoint](**req.view_args)   file "./conjugate.py", line 169, in conjugate     translation in get_translations(lang, verb)],   file "./conjugate.py", line 80, in get_translations     entry in session.query(translation).filter_by(lang=lang, english=english):   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2515, in __iter__     return self._execute_and_instances(context)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2530, in _execute_and_instances     result = conn.execute(querycontext.statement, self._params)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 914, in execute     return meth(self, multiparams, params)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/sql/elements.py", line 323, in _execute_on_connection     return connection._execute_clauseelement(self, multiparams, params)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1010, in _execute_clauseelement     compiled_sql, distilled_params   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1078, in _execute_context     none, none)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1339, in _handle_dbapi_exception     exc_info   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/util/compat.py", line 199, in raise_from_cause     reraise(type(exception), exception, tb=exc_tb)   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1071, in _execute_context     conn = self._revalidate_connection()   file "/home/dsaltares/conjugate/env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 391, in _revalidate_connection     "can't reconnect until invalid " statementerror: (sqlalchemy.exc.invalidrequesterror) can't reconnect until invalid transaction rolled [sql: u'select translations.lang translations_lang, translat    ions.verb translations_verb, translations.english translations_english, translations.description translations_description \nfrom translations \nwhere translations.l    ang = %s , translations.english = %s'] [parameters: [immutabledict({})]]

the remaining 25% query works fine , returns expected data. these queries spaced in time, it's not trashing service.

the query crashing @ is

try:     entry in session.query(translation).filter_by(lang=lang, english=english):         translations.append({             'lang': lang,             'english': english,             'verb': entry.verb,             'description': entry.description         }) except:     app.logger.error('error querying translations (%s, %s)\n%s' % (lang, english, traceback.format_exc()))     raise

the translation mapper:

from sqlalchemy.ext.declarative import declarative_base sqlalchemy import column, integer, string  base = declarative_base()  class translation(base):     __tablename__ = 'translations'      lang = column(string(10), primary_key=true)     verb = column(string(25), primary_key=true)     english = column(string(25), primary_key=true)     description = column(string)      def __repr__(self):         return "<translation(lang='%s', verb='%s', english='%s'>" % (self.lang, self.verb, self.english)

any ideas may be? need provide more information?


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