[mypyc] Use smaller default buffer for BytesWriter #20574
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This seems to make allocations and/or frees a lot faster, at least
in this microbenchmark (on 3.14 it's over 2x faster with the smaller
buffer):
```
def bench(b: bytes, n: int) -> None:
for x in range(n):
w = BytesWriter()
w.write(b)
w.getvalue()
n = 30 * 1000 * 1000
b = b"foo"
bench(b, n)
```
p-sawicki
approved these changes
Jan 13, 2026
Member
|
Hm, I am curious would it make sense to make the same change in |
Member
|
Oh, nvm, your benchmark is for very small bytes object, I guess typical cache files are usually at least 1-2 KB. So maybe it is not relevant for |
Collaborator
Author
|
Yeah, this only helps with very small bytes objects. |
michaelm-openai
pushed a commit
to michaelm-openai/mypy
that referenced
this pull request
Jan 16, 2026
This seems to make allocations and/or frees a lot faster, at least in
this microbenchmark (on 3.14 it's over 2x faster with the smaller
buffer):
```
def bench(b: bytes, n: int) -> None:
for x in range(n):
w = BytesWriter()
w.write(b)
w.getvalue()
n = 30 * 1000 * 1000
b = b"foo"
bench(b, n)
```
michaelm-openai
pushed a commit
to michaelm-openai/mypy
that referenced
this pull request
Jan 16, 2026
This seems to make allocations and/or frees a lot faster, at least in
this microbenchmark (on 3.14 it's over 2x faster with the smaller
buffer):
```
def bench(b: bytes, n: int) -> None:
for x in range(n):
w = BytesWriter()
w.write(b)
w.getvalue()
n = 30 * 1000 * 1000
b = b"foo"
bench(b, n)
```
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This seems to make allocations and/or frees a lot faster, at least in this microbenchmark (on 3.14 it's over 2x faster with the smaller buffer):