Pickling models is slow in alpha versions

[Alexander Schepanovski]

When pickling Django models in alpha version get_version() creates a git subprocess, which is very slow. I suggest memoizing get_version().

[Alexander Schepanovski]

Created pull request ​https://github.com/django/django/pull/2829

[loic84]

+1 although I'd only wrap get_git_changeset with lru_cache.

Marking as a release blocker for 1.8 since this is a regression from #21430.

[anonymous]

Moved @lru_cache() to get_git_changeset().

[Tim Graham <timograham@…>]

In 80f4487d17a0040e9be35e7ee6ac478bafe6504a:

Fixed #22867 -- Memoized django.utils.version.get_git_changeset().

This improves pickling speed in prelease versions of Django; refs #21430.

[Aymeric Augustin <aymeric.augustin@…>]

In 01399fa0aaa817281c77bbb4b7d82c6c8487c916:

Revert "Fixed #22867 -- Memoized django.utils.version.get_git_changeset()."

This reverts commit 80f4487 temporarily, because that commit prevented
the djangoproject.com server from building the docs, because it still
uses Python 2.6.

[Aymeric Augustin]

While this commit was correct, I had to revert it because it broke the docs builds, which are still running on Python 2.6.

We need to upgrade the djangoproject.com server before we can push this change. Sorry for the inconvenience.

[loic84]

Upgrading Python 2.6 which is EOL and recommitting this fix is the ideal course of action.

However if we don't manage to do so within a few of days, I'd suggest we go with a stopgap solution like ​https://gist.github.com/313430836d20006916c4f.

The regression could be quite severe to anyone caching large querysets since we'd be starting a process for each model.

[Loic Bistuer <loic.bistuer@…>]

In f07735c619c121d8785082972acd8fbad8b236af:

Fixed #22867 -- Memoized django.utils.version.get_git_changeset().

This follows commits 80f4487 and 01399fa; original patch had to be
reverted because it wasn't Python 2.6 compatible and we need it to
be in order to build docs on the djangoproject.com server.

This fix should be replaced by @lru_cache as soon as we drop
Python 2.6 compatibility.

Thanks Florian Apolloner for the review and Alexander Schepanovski
for the original patch.

[loic84]

Reopening as a "Cleanup/optimization" so we don't lose track of replacing this temporary fix with lru_cache.

[Tim Graham]

We are just waiting on the new server.

[Tim Graham <timograham@…>]

In 2c681e8a8c453b1691219eace7ed5dc636e37948:

Fixed #22867 -- Memoized django.utils.version.get_git_changeset().

Restored original fix that had to be removed because the old djangoproject
server was still using Python 2.6.