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Fixed #33865 -- Optimized LimitedStream wrapper.

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The current implementation of LimitedStream is slow because .read()
performs an extra copy into a buffer and .readline() performs two
extra copies. The stream being wrapped is already typically a BytesIO
object so this is unnecessary.

This implementation has largely been untouched for 12 years and,
inspired by a simpler implementation in werkzeug, it was possible to
achieve the following performance improvement:

LimitedStream.read() (single line):
  Mean +- std dev: [bench_limitedstream-main] 286 ns +- 6 ns
  -> [bench_limitedstream-patch] 227 ns +- 6 ns: 1.26x faster
LimitedStream.readline() (single line):
  Mean +- std dev: [bench_limitedstream-main] 507 ns +- 11 ns
  -> [bench_limitedstream-patch] 232 ns +- 8 ns: 2.18x faster
LimitedStream.read(8192) (single line):
  Mean +- std dev: [bench_limitedstream-main] 360 ns +- 8 ns
  -> [bench_limitedstream-patch] 297 ns +- 6 ns: 1.21x faster
LimitedStream.readline(8192) (single line):
  Mean +- std dev: [bench_limitedstream-main] 602 ns +- 10 ns
  -> [bench_limitedstream-patch] 305 ns +- 10 ns: 1.98x faster
LimitedStream.read() (multiple lines):
  Mean +- std dev: [bench_limitedstream-main] 290 ns +- 5 ns
  -> [bench_limitedstream-patch] 236 ns +- 6 ns: 1.23x faster
LimitedStream.readline() (multiple lines):
  Mean +- std dev: [bench_limitedstream-main] 517 ns +- 19 ns
  -> [bench_limitedstream-patch] 239 ns +- 7 ns: 2.16x faster
LimitedStream.read(8192) (multiple lines):
  Mean +- std dev: [bench_limitedstream-main] 363 ns +- 8 ns
  -> [bench_limitedstream-patch] 311 ns +- 11 ns: 1.17x faster
LimitedStream.readline(8192) (multiple lines):
  Mean +- std dev: [bench_limitedstream-main] 601 ns +- 12 ns
  -> [bench_limitedstream-patch] 308 ns +- 7 ns: 1.95x faster

Geometric mean: 1.59x faster
This commit is contained in:
Nick Pope
2022-07-22 21:08:10 +01:00
committed by Mariusz Felisiak
parent 57f5669d23
commit b47f2f5b90
4 changed files with 43 additions and 49 deletions
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4
docs/releases/4.2.txt
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@@ -523,6 +523,10 @@ Miscellaneous
.. _`redis-py`: https://pypi.org/project/redis/
* Manually instantiated ``WSGIRequest`` objects must be provided a file-like
object for ``wsgi.input``. Previously, Django was more lax than the expected
behavior as specified by the WSGI specification.
.. _deprecated-features-4.2:
Features deprecated in 4.2