[django/django] 75ec1f: Clarifed table rewrites in migration docs.

[GitHub]

Branch: refs/heads/master
Home: https://github.com/django/django
Commit: 75ec1fdf16ac76b5c945aef1cdb9a1e104369c85
https://github.com/django/django/commit/75ec1fdf16ac76b5c945aef1cdb9a1e104369c85
Author: Marti Raudsepp <ma...@juffo.org>
Date: 2013-12-14 (Sat, 14 Dec 2013)

Changed paths:
M docs/topics/migrations.txt

Log Message:
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Clarifed table rewrites in migration docs.

Small nitpicks. All column-related ALTER TABLE commands take an
exclusive table lock in PostgreSQL. The difference is that adding a
column without default doesn't cause a table rewrite, so the lock is
held only for a short time.

The time taken is more accurately proportional to table size, not row
count.