Changes between Version 16 and Version 17 of new_meta_api

Timestamp:

Jul 11, 2014, 8:52:52 AM (10 years ago)

Author:

pirosb3

Comment:

--

new_meta_api

@@ -302 +302 @@
 Our final iteration was to add all the field types as flags to get_field. By making m2m as first parameter, we avoid breaking existing implementations
 and maintain a similarity with the 'get_fields' API.
+
+=== Performance
+Throughout my project I have always kept an eye on performance. Throughout the development of my API I have refactored often and always looked for
+bottlenecks using cProfile. I am happy to say no major decrease in speed has happened, and the new implementation does a couple of optimizations
+that were not present in the old system. Said this, I prefer to not comment on performance but just to show the benchmarks. It will be the core
+team to decide if this is feasible or not.
+
+=== Main optimization points
+
+==== Compute inverse relation map on first access
+In order to find related objects, the current implementation does the following
+
+{{{
+    for each model in apps
+       for each field in model
+          if field is a related object:
+             if field is related to self:
+                 add to related_objects
+}}}
+REF: https://github.com/django/django/blob/master/django/db/models/options.py#L488
+
+This tends to be expensive depending on the setup, but results in a O(models * fields) complexity. We can increase performance by
+computing a inverse relation map on first access. This is done only **once**, not once per model
+
+REF: https://github.com/PirosB3/django/blob/soc2014_meta_refactor_upgrade_flags_get_field/django/apps/registry.py#L176
+
+In this way we have a map of model -> [related_object, related_object, ..] and computing a hash lookup is O(1).
+
+https://github.com/PirosB3/django/blob/soc2014_meta_refactor_upgrade_flags_get_field/django/db/models/options.py#L423
+
+Now, only 1 small loop is needed.
+
+==== Benchmarks
+Here is a benchmarks table. It is benchmarking soc2014_meta_refactor_upgrade_flags_get_field (68dc11708eb2170540729b71db6bcaf4c46d6504)
+against django/master
+
+https://gist.github.com/PirosB3/35a9231ee0214427321d