bpo-41486: zlib uses an UINT32_MAX sliding window for the output buffer #26143
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These funtions have an initial output buffer size parameter: - zlib.decompress(data, /, wbits=MAX_WBITS, bufsize=DEF_BUF_SIZE) - zlib.Decompress.flush([length]) If the initial size > UINT32_MAX, use an UINT32_MAX sliding window, instead of clamping to UINT32_MAX. Speed up when (the initial size == the actual size).
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@gpshead See this comment for details. I had used half a month to polish this patch, mainly trying various code styles. The code has been tested with this script: import zlib, time, random
_1G = 1024*1024*1024
UINT32_MAX = 0xFFFF_FFFF
def test(DATA_SIZE, INIT_BUFF_SIZES):
b = random.choice((b'a', b'b', b'c', b'd'))
raw_dat = b * DATA_SIZE
t1=time.perf_counter()
compressed_dat = zlib.compress(raw_dat, 1)
t2=time.perf_counter()
del raw_dat
print(f'compressed size: {len(compressed_dat)}, time: {t2-t1:.5f}')
for init_size in INIT_BUFF_SIZES:
t1=time.perf_counter()
decompressed_dat = zlib.decompress(compressed_dat, bufsize=init_size)
t2=time.perf_counter()
assert len(decompressed_dat) == DATA_SIZE
assert decompressed_dat.count(b) == DATA_SIZE
del decompressed_dat
print(f'data size: {DATA_SIZE:>8}, init buff size: {init_size:>8}, time: {t2-t1:.5f}')
print()
SIZE = _1G
test(SIZE, (100, SIZE, SIZE+1, UINT32_MAX, UINT32_MAX+1))
SIZE = UINT32_MAX
test(SIZE, (100, SIZE, SIZE+1, 2*UINT32_MAX+1))
SIZE = 10*_1G
test(SIZE, (_1G, SIZE-1, SIZE, SIZE+1, UINT32_MAX, UINT32_MAX+1,
2*UINT32_MAX+1, 3*UINT32_MAX+1, 4*UINT32_MAX+1))
SIZE = 20*_1G
test(SIZE, (3*_1G, SIZE-1, SIZE, SIZE+1, UINT32_MAX, UINT32_MAX+1,
2*UINT32_MAX+1, 3*UINT32_MAX+1, 4*UINT32_MAX+1, 5*UINT32_MAX+1, 6*UINT32_MAX+1)) |
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This PR is stale because it has been open for 30 days with no activity. |
gpshead
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needs backport to 3.10
gpshead
approved these changes
Jul 5, 2021
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Thanks @animalize for the PR, and @gpshead for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10. |
miss-islington
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Jul 5, 2021
…er (pythonGH-26143) * zlib uses an UINT32_MAX sliding window for the output buffer These funtions have an initial output buffer size parameter: - zlib.decompress(data, /, wbits=MAX_WBITS, bufsize=DEF_BUF_SIZE) - zlib.Decompress.flush([length]) If the initial size > UINT32_MAX, use an UINT32_MAX sliding window, instead of clamping to UINT32_MAX. Speed up when (the initial size == the actual size). This fixes a memory consumption and copying performance regression in earlier 3.10 beta releases if someone used an output buffer larger than 4GiB with zlib.decompress. Reviewed-by: Gregory P. Smith (cherry picked from commit a9a69bb) Co-authored-by: Ma Lin <animalize@users.noreply.github.com>
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GH-27025 is a backport of this pull request to the 3.10 branch. |
miss-islington
added a commit
that referenced
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Jul 5, 2021
…er (GH-26143) * zlib uses an UINT32_MAX sliding window for the output buffer These funtions have an initial output buffer size parameter: - zlib.decompress(data, /, wbits=MAX_WBITS, bufsize=DEF_BUF_SIZE) - zlib.Decompress.flush([length]) If the initial size > UINT32_MAX, use an UINT32_MAX sliding window, instead of clamping to UINT32_MAX. Speed up when (the initial size == the actual size). This fixes a memory consumption and copying performance regression in earlier 3.10 beta releases if someone used an output buffer larger than 4GiB with zlib.decompress. Reviewed-by: Gregory P. Smith (cherry picked from commit a9a69bb) Co-authored-by: Ma Lin <animalize@users.noreply.github.com>
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These funtions have an initial output buffer size parameter:
If the initial size >
UINT32_MAX, use anUINT32_MAXsliding window, instead of clamping toUINT32_MAX.Speed up when (the initial size == the actual size).
https://bugs.python.org/issue41486