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[2.1.x] Fixed #29685 -- Added QuerySet.explain() to the database optimization docs.

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Backport of b042ab897636987701d3a35d6b566c6bef9d6ea2 from master
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Tom Forbes 2018-08-18 14:22:21 +01:00 committed by Tim Graham
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1 changed files with 11 additions and 2 deletions
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docs/topics/db/optimization.txt
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@ -11,8 +11,9 @@ Profile first
============= =============
As general programming practice, this goes without saying. Find out :ref:`what As general programming practice, this goes without saying. Find out :ref:`what
queries you are doing and what they are costing you queries you are doing and what they are costing you <faq-see-raw-sql-queries>`.
<faq-see-raw-sql-queries>`. You may also want to use an external project like Use :meth:`.QuerySet.explain` to understand how specific ``QuerySet``\s are
executed by your database. You may also want to use an external project like
django-debug-toolbar_, or a tool that monitors your database directly. django-debug-toolbar_, or a tool that monitors your database directly.
Remember that you may be optimizing for speed or memory or both, depending on Remember that you may be optimizing for speed or memory or both, depending on
@ -114,6 +115,14 @@ When you have a lot of objects, the caching behavior of the ``QuerySet`` can
cause a large amount of memory to be used. In this case, cause a large amount of memory to be used. In this case,
:meth:`~django.db.models.query.QuerySet.iterator()` may help. :meth:`~django.db.models.query.QuerySet.iterator()` may help.
Use ``explain()``
-----------------
:meth:`.QuerySet.explain` gives you detailed information about how the database
executes a query, including indexes and joins that are used. These details may
help you find queries that could be rewritten more efficiently, or identify
indexes that could be added to improve performance.
Do database work in the database rather than in Python Do database work in the database rather than in Python
====================================================== ======================================================