Opened 16 months ago

Last modified 14 months ago

#22330 new Cleanup/optimization

Model.__reduce__() includes cached lookups

Reported by: patrys Owned by: nobody
Component: Database layer (models, ORM) Version: 1.6
Severity: Normal Keywords:
Cc: Triage Stage: Accepted
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

If you try to pickle an object after accessing any of its related instances, its __dict__ will contain references to those instances and will cause them to be pickled as part of your object.

Pickling them can cause additional instances to be traversed and can result in an unexpectedly large number of objects being included. These will be pickled/unpickled as a single chunk and I assume the unpickled instance will continue to use its cached instances which may lead to surprising results (values not reflecting current DB state).

Pickling additional instances can cause relation traversal to cache additional reverse lookups thus modifying an instance's __dict__ while it is being pickled. This results in:

RuntimeError: dictionary changed size during iteration

Change History (1)

comment:1 Changed 14 months ago by timo

  • Component changed from Uncategorized to Database layer (models, ORM)
  • Needs documentation unset
  • Needs tests unset
  • Patch needs improvement unset
  • Triage Stage changed from Unreviewed to Accepted
  • Type changed from Uncategorized to Cleanup/optimization

I am not sure of the expected behavior. If we don't make a change here, we should at least document like we've done for QuerySet pickling.

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