#15625: MultiValueDictKeyError exception has large performance penalty
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Reporter: margieroginski | Owner: nobody
Status: new | Milestone:
Component: Uncategorized | Version: 1.2
Keywords: | Triage Stage: Unreviewed
Has patch: 0 |
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I am seeing a large potential performance penalty due to a string argument
representing the entire POST dict getting created when a key is not found
in the POST dict.
In datastructures.py, in class !MultiValueDict, {{{__getitem__()}}} has
the following code:
{{{
try:
list_ = super(!MultiValueDict, self).__getitem__(key)
except !KeyError:
raise !MultiValueDictKeyError("Key %r not found in %r" % (key,
self))
}}}
During form validation, this exception is raised for each field/key not
found in the POST dict. If the POST dict is very large, the %r associated
with self is very large and can have a very significant time penalty. In
a case where I had 300 of these exceptions, the time penalty of creating
this string was almost 2 seconds.
It is not that unusual to have POST keys missing that are checked in this
way. Here are a few of the common cases I've seen:
1. checkboxes that are unchecked
2. url arguments that could be POSTED but which are omitted
3. fields that are dynamic - ie, they may not be there unless some client
code creates them.
Do we need to provide a string argument at all in this case, given the
potential time penalty and the frequency of getting values from the POST
dict?
--
Ticket URL: <http://code.djangoproject.com/ticket/15625>
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