New submission from Terry J. Reedy <[email protected]>:
https://metarabbit.wordpress.com/2018/02/05/pythons-weak-performance-matters/,
a blog post on cpython speed, clains "deleting a set of 1 billion strings takes
>12 hours". (No other details provided.)
I don't have the 100+ gigabytes of ram needed to confirm this, but with
installed 64 bit 3.7.0b1 with Win10 and 12 gigabyes, I confirmed that there is
a pronounced super-linear growth in string set deletion (unlike with an integer
set). At least half of ram was available.
Seconds to create and delete sets
millions integers strings
of items create delete create delete
1 .08 .02 .36 .08
2 .15 .03 .75 .17
4 .30 .06 1.55 .36
8 .61 .12 3.18 .76
16 1.22 .24 6.48 1.80 < slightly more than double
32 2.4 .50 13.6 5.56 < more than triple
64 4.9 1.04 28 19 < nearly quadruple
128 10.9 2.25 <too large>
100 56 80 < quadruple with 1.5 x size
For 100 million strings, I got about the same 56 and 80 seconds when timing
with a clock, without the timeit gc suppression. I interrupted the 128M string
run after several minutes. Even if there is swapping to disk during creation,
I would not expect it during deletion.
The timeit code:
import timeit
for i in (1,2,4,8,16,32,64,128):
print(i, 'int')
print(timeit.Timer(f's = {{n for n in range({i}*1000000)}}')
.timeit(number=1))
print(timeit.Timer('del s', f's = {{n for n in range({i}*1000000)}}')
.timeit(number=1))
for i in (1,2,4,8,16,32,64,100):
print(i, 'str')
print(timeit.Timer(f's = {{str(n) for n in range({i}*1000000)}}')
.timeit(number=1))
print(timeit.Timer('del s', f's = {{str(n) for n in range({i}*1000000)}}')
.timeit(number=1))
Raymond, I believe you monitor the set implementation, and I know Victor is
interested in timing and performance.
----------
messages: 312188
nosy: rhettinger, terry.reedy, vstinner
priority: normal
severity: normal
stage: needs patch
status: open
title: Deletion of large sets of strings is extra slow
type: performance
versions: Python 3.7, Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue32846>
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