New submission from Ma Lin <malin...@163.com>:
These changes reduce sizeof(match_context):
- 32-bit build: 36 bytes, no change.
- 64-bit build: 72 bytes -> 56 bytes.
sre uses stack and `match_context` struct to simulate recursive call, smaller
struct brings:
- deeper recursive call
- less memory consume
- less memory realloc
Here is a test, if limit the stack size to 1 GiB, the max available value of n
is:
re.match(r'(ab)*', n * 'ab') # need to save MARKs
72 bytes: n = 11,184,808
64 bytes: n = 12,201,609
56 bytes: n = 13,421,770
re.match(r'(?:ab)*', n * 'ab') # no need to save MARKs
72 bytes: n = 13,421,770
64 bytes: n = 14,913,078
56 bytes: n = 16,777,213
1,073,741,823 capturing groups should enough for almost all users.
If limit it to 16,383 (2-byte integer), the context size may reduce more. But
maybe some patterns generated by program will have more than this number of
capturing groups.
1️⃣Performance:
Before
regex_dna: Mean +- std dev: 149 ms +- 1 ms
regex_effbot: Mean +- std dev: 2.22 ms +- 0.02 ms
regex_v8: Mean +- std dev: 22.3 ms +- 0.1 ms
my benchmark[1]: 13.9 sec +- 0.0 sec
Commit 1. limit the maximum capture group to 1,073,741,823
regex_dna: Mean +- std dev: 150 ms +- 1 ms
regex_effbot: Mean +- std dev: 2.16 ms +- 0.02 ms
regex_v8: Mean +- std dev: 22.3 ms +- 0.1 ms
my benchmark: 13.8 sec +- 0.0 sec
Commit 2. further reduce sizeof(SRE(match_context))
regex_dna: Mean +- std dev: 150 ms +- 1 ms
regex_effbot: Mean +- std dev: 2.16 ms +- 0.02 ms
regex_v8: Mean +- std dev: 22.2 ms +- 0.1 ms
my benchmark: 13.8 sec +- 0.1 sec
If further change the types of toplevel/jump from int to char, in 32-bit build
sizeof(match_context) will be reduced from 36 to 32 (In 64-bit build still 56).
But it's slower on 64-bit build, so I didn't adopt it:
regex_dna: Mean +- std dev: 150 ms +- 1 ms
regex_effbot: Mean +- std dev: 2.18 ms +- 0.01 ms
regex_v8: Mean +- std dev: 22.4 ms +- 0.1 ms
my benchmark: 14.1 sec +- 0.0 sec
2️⃣ The type of match_context.count is Py_ssize_t
- If change it to 4-byte integer, need to modify some engine code.
- If keep it as Py_ssize_t, SRE_MAXREPEAT may >= 4 GiB in future versions.
Currently SRE_MAXREPEAT can't >= 4 GiB.
So the type of match_context.count is unchanged.
[1] My re benchmark, it uses 16 patterns to process 100 MiB text data:
https://github.com/animalize/re_benchmarks
----------
components: Library (Lib)
messages: 416960
nosy: ezio.melotti, malin, mrabarnett, serhiy.storchaka
priority: normal
severity: normal
status: open
title: re: limit the maximum capturing group to 1,073,741,823, reduce
sizeof(match_context).
type: resource usage
versions: Python 3.11
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue47256>
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