#15361: QuerySet.get() should use LIMIT 2
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Reporter: mbertheau | Owner:
mmcnickle
Status: new | Milestone:
Component: Database layer (models, ORM) | Version: 1.2
Resolution: | Keywords:
QuerySet get limit MultipleObjectsReturned
Triage Stage: Accepted | Has patch: 1
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 |
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Changes (by mmcnickle):
* owner: nobody => mmcnickle
Comment:
The concern that this change may make the get() slower may be valid, but
one thing is for sure, that benchmark is inadequate for anything but huge
performance regressions. I'm able to produce "Significant" slower results
by running 2 identical versions of django:
{{{
Running all benchmarks
Control: Django 1.3 beta 1 (in django-control)
Experiment: Django 1.3 beta 1 (in django-experiment)
Running 'query_get' benchmark ...
Min: 0.020000 -> 0.020000: no change
Avg: 0.022400 -> 0.024800: 1.1071x slower
Significant (t=-2.556039)
Stddev: 0.00431 -> 0.00505: 1.1698x larger (N = 50)
}}}
The telling fact is that these "significant" results are transient,
differing from run to run.
I'll write a benchmark that will properly stress the query.get() and see
if:
a) There is a performance regression for pk (or other fields with unique
constraints) lookups[[BR]]
b) There is a performance increase for non-indexed, large match lookups.
If (b) and not (a), it's a +1.[[BR]]
If (a) and (b), it's probably a -1, given the more usual case in (a)[[BR]]
If (a) and not (b), -1
--
Ticket URL: <http://code.djangoproject.com/ticket/15361#comment:7>
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