Assign changed localized value directly

[topaxi]

Calling self.__dict__.update(self) causes repetetive iterations over all configured language keys. The default in Django is 99, which causes this update to grow quadratic.

Stumbled upon this for a larger object graph (~500+ entities), where each entity has multiple localized fields.

repro.py

"""Reproduces O(n^2) LocalizedValue construction high language count (99,
django default).
"""

import time

import django
from django.conf import settings
from localized_fields.value import LocalizedValue

settings.configure(USE_I18N=True, LANGUAGE_CODE="lang0", LANGUAGES=[])
django.setup()

LANGUAGE_COUNT = 99

settings.LANGUAGES = [(f"lang{i}", f"Language {i}") for i in range(LANGUAGE_COUNT)]
settings.LANGUAGE_CODE = "lang0"

FIELDS_PER_ENTITY = 10
DB_VALUE = {"lang0": "some value", "lang1": "ein Wert"}


def build_entity():
    return [LocalizedValue(DB_VALUE) for _ in range(FIELDS_PER_ENTITY)]


def time_graph(num_entities):
    start = time.perf_counter()
    for _ in range(num_entities):
        build_entity()
    return time.perf_counter() - start


def run(label):
    print(
        f"\n{label} ({len(settings.LANGUAGES)} languages, "
        f"{FIELDS_PER_ENTITY} localized fields/entity)"
    )
    print(f"{'entities':>10} {'seconds':>12} {'ms/entity':>12}")
    for n in (10, 50, 100, 500, 1000, 2000):
        elapsed = time_graph(n)
        print(f"{n:>10} {elapsed:>12.4f} {elapsed / n * 1000:>12.4f}")


run("before fix (original LocalizedValue.set)")


def fixed_set(self, language, value):
    """Only touch the key that changed, instead of re-copying the whole dict."""
    self[language] = value
    self.__dict__[language] = value
    return self


LocalizedValue.set = fixed_set

run("after fix (patched LocalizedValue.set)")

repro.py summary with 99 languages

before fix (original LocalizedValue.set) (99 languages, 10 localized fields/entity)
  entities      seconds    ms/entity
        10       0.0420       4.2035
        50       0.2104       4.2073
       100       0.4197       4.1967
       500       2.1028       4.2055
      1000       4.2038       4.2038
      2000       4.6492       2.3246

after fix (patched LocalizedValue.set) (99 languages, 10 localized fields/entity)
  entities      seconds    ms/entity
        10       0.0027       0.2707
        50       0.0133       0.2658
       100       0.0268       0.2682
       500       0.1338       0.2676
      1000       0.2676       0.2676
      2000       0.5359       0.2679

repro.py summary with 3 languages (no regression)

before fix (original LocalizedValue.set) (3 languages, 10 localized fields/entity)
  entities      seconds    ms/entity
        10       0.0005       0.0499
        50       0.0024       0.0477
       100       0.0045       0.0445
       500       0.0228       0.0456
      1000       0.0436       0.0436
      2000       0.0891       0.0445

after fix (patched LocalizedValue.set) (3 languages, 10 localized fields/entity)
  entities      seconds    ms/entity
        10       0.0003       0.0331
        50       0.0015       0.0310
       100       0.0030       0.0299
       500       0.0153       0.0306
      1000       0.0306       0.0306
      2000       0.0615       0.0307