On 07/22/2016 05:13 PM, Simon King wrote:
On Fri, Jul 22, 2016 at 3:25 PM, TomS. <pidev...@gmail.com> wrote:
On 07/19/2016 06:41 PM, Mike Bayer wrote:
On 07/19/2016 11:51 AM, TomS. wrote:
Hi,
We have Flask app which uses SQLAlchemy. Weird error started to happen
recently. The difficulty is that we can't reproduce the error (/figure
out conditions causing issue) - maybe someone could help. Any hints/tips
would be appreciated.
There is a part in the code which constructs IN in SQL:
MyModel.id.in_(my_ids)
For some cases my_ids is an empty list. It works without any problems,
but after some time the same query (using empty list) starts to raise an
exception:
SAWarning: The IN-predicate on "MyModel.id" was invoked with an empty
sequence. This results in a contradiction, which nonetheless can be
expensive to evaluate. Consider alternative strategies for improved
performance.
After restarting app, everything works again.
The question is - why this exception is not risen always (although we
tried to run app with empty list directly), but after some time of app
execution (~1 day)?
It's not an exception, it's a warning. Python warnings by default emit only
once, see:
https://docs.python.org/2/library/warnings.html#the-warnings-filter
Ok, this is the explanation why it doesn't show up regularly. Thank you.
I don't know why SAWarning is treated as error. Here is the log:
2016-07-21 13:58:14,108 ERROR: Exception on /own [GET]
Traceback (most recent call last):
[...]
File
"/home/developer/.virtualenvs/rest/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
line 1297, in warn
warnings.warn(msg, exc.SAWarning, stacklevel=2)
SAWarning: The IN-predicate on "MyModel.id" was invoked with an empty
sequence. This results in a contradiction, which nonetheless can be
expensive to evaluate.
I will also ask on Flask group, but maybe you know the reason - Flask config
regarding logging is as follow:
import logging
from logging.handlers import RotatingFileHandler
logger_file_handler = RotatingFileHandler('my.log', maxBytes=1024 * 1024 *
100, backupCount=20)
logger_file_handler.setLevel(logging.DEBUG)
logger_formatter = logging.Formatter(u'%(asctime)s %(levelname)s:
%(message)s')
logger_file_handler.setFormatter(logger_formatter)
logging.captureWarnings(True)
app.logger.addHandler(logger_file_handler)
app.logger.setLevel(logging.DEBUG)
There is no code which change behavior (by filter) of SAWarning to 'error'
...
The python warnings system is completely separate from the logging
system. Whether or not a particular warning is turned into an
exception is driven by the "warnings filter":
https://docs.python.org/2/library/warnings.html#the-warnings-filter
I think you must be configuring the warnings filter somewhere, because
by default this shouldn't raise an exception.
Yes, you were right. I finally found the source of the issue. There was
link in the part of the code which set warnings to behave like the
exceptions. But this code was not executed always but under certain
conditions. That was the first issue with debuging. The second one - the
fact that it is web app which is run using many processes. So on some
"process" code was already executed while on others not.
Thank you for the ideas!
Simon
Cheers!
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