#32940: Consider removing unused/unnecessary functionality in tree.Node.add
------------------------------------------------+------------------------
Reporter: Keryn Knight | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Utilities | Version: dev
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 1
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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I'm proposing for discussion the removal of 2 things within the `Node.add`
method, or at least further investigation on why it's ''not'' possible to
do so; those 2 bits are outlined immediately below.
If we instrument the `Node.add` method, used by `query_utils.Q` and
`where.WhereNode` extensively, like so:
{{{
...
if data in self.children:
print('v- data existed')
traceback.print_stack()
if self.connector == conn_type and data in self.children:
print('^- data existed and connector matched')
return data
if not squash:
print('<- squash is not Truthy')
self.children.append(data)
return data
...
}}}
and run the test suite (or as much as I'm able easily):
{{{
...
Ran 14834 tests in 453.388s
OK (skipped=1188, expected failures=4)
}}}
We will find that the `data in self.children` barely registers as
tested/used, and `squash` is entirely unused (unless those 1188 tests hide
the truth).
Having separately instrumented the add method previously to check the
number of ''calls'' by class type, it appears as below:
- `1493` calls to `Q.add` of which `0` have a `data in children` match.
- `2` calls to `Node.add` of which `1` is a `data in children` match.
- `210862` calls to `WhereNode.add` of which `2` are a `data in children
match.
But of all of those matches, the connector is never the same, so it never
does that return early expected optimisation.
The tests which exercise those 3 matches are:
- `tests.queries.tests.DisjunctiveFilterTests.test_ticket8283`
- `tests.queries.tests.Queries4Tests.test_combine_or_filter_reuse`
-
`tests.utils_tests.test_tree.NodeTests.test_add_eq_child_mixed_connector`
The last of those is ''intentionally'' making sure that it ''does'' get
added due to the connector difference.
The first two, as they could affect where clause pushdown & merging, or
cause different query plans due to repeats, we should check to make sure
that the queries (additionally to the results) remain the same before and
after by doing the following back of the napkin job for each of them:
{{{
self.assertEqual(
str(x.query),
"???"
)
}}}
and confirm that they remain the same (they do), which are:
{{{
'SELECT "queries_extrainfo"."id", "queries_extrainfo"."info",
"queries_extrainfo"."note_id", "queries_extrainfo"."value",
"queries_extrainfo"."date_id", "queries_extrainfo"."filterable" FROM
"queries_extrainfo" WHERE (("queries_extrainfo"."note_id" = 1 OR
"queries_extrainfo"."info" = e2) AND "queries_extrainfo"."note_id" = 1)
ORDER BY "queries_extrainfo"."info" ASC';
'SELECT "queries_extrainfo"."id", "queries_extrainfo"."info",
"queries_extrainfo"."note_id", "queries_extrainfo"."value",
"queries_extrainfo"."date_id", "queries_extrainfo"."filterable" FROM
"queries_extrainfo" WHERE (("queries_extrainfo"."info" = e2 OR
"queries_extrainfo"."note_id" = 1) AND "queries_extrainfo"."note_id" = 1)
ORDER BY "queries_extrainfo"."info" ASC';
'SELECT "queries_author"."id", "queries_author"."name",
"queries_author"."num", "queries_author"."extra_id" FROM "queries_author"
WHERE (("queries_author"."name" = a1 OR "queries_author"."name" = a3) AND
"queries_author"."name" = a1)';
}}}
Removing the `data in self.children` check should be a small optimisation
win because it's an `O(n)` scan across the entire list of direct children,
and uses the `Node.__eq__` method which does an equality scan on it's own
children (so grandchildren).
{{{
In [2]: %%timeit
...: x = Q(('a', 1), ('b', 2), c=3, d=4, b=1)
...: y = Q(aa=1, bb=2, cc=3)
...: x.add(y, Q.OR)
4.81 µs ± 16.1 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
}}}
after removing:
{{{
4.66 µs ± 21.1 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
}}}
It's worth noting that the concept of checking `data in self.children` is
semi-flawed anyway, because `Q(('a', 1), a=2)` or `Q(('a', 1), ('a', 2))`
very ''simply'' allow duplicate entries to occur immediately and up-front.
I have a patch which I'll push up shortly once I've tidied it of all my
instrumentation and `pdb` usage. The hope is that the entire CI passes, if
it doesn't this is all moot :)
--
Ticket URL: <https://code.djangoproject.com/ticket/32940>
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