[PATCH 4 of 5 V4] match: avoid translating glob to matcher multiple times for large sets
Boris FELD
boris.feld at octobus.net
Sun Dec 2 10:26:25 EST 2018
On 02/12/2018 01:38, Martin von Zweigbergk via Mercurial-devel wrote:
> I have a few more questions. Sorry I didn't notice last time (because
> I only considered the higher-level issues).
>
> On Sat, Dec 1, 2018 at 4:07 AM Boris Feld <boris.feld at octobus.net
> <mailto:boris.feld at octobus.net>> wrote:
>
> # HG changeset patch
> # User Boris Feld <boris.feld at octobus.net
> <mailto:boris.feld at octobus.net>>
> # Date 1542916922 -3600
> # Thu Nov 22 21:02:02 2018 +0100
> # Node ID 0a28ff17100a67c21a99ef363f15aef09e4dfa8b
> # Parent 066912081df7b43ed271bea4475e35661e16c1cf
> # EXP-Topic perf-ignore
> # Available At https://bitbucket.org/octobus/mercurial-devel/
> # hg pull
> https://bitbucket.org/octobus/mercurial-devel/ -r 0a28ff17100a
> match: avoid translating glob to matcher multiple times for large sets
>
> For hgignore with many globs, the resulting regexp might not fit
> under the 20K
> length limit. So the patterns need to be broken up in smaller pieces.
>
> Before this change, the logic was re-starting the full process
> from scratch
> for each smaller pieces, including the translation of globs into
> regexp.
> Effectively doing the work over and over.
>
> If the 20K limit is reached, we are likely in a case where there
> is many such
> glob, so exporting them is especially expensive and we should be
> careful not
> to do that work more than once.
>
> To work around this, we now translate glob to regexp once and for
> all. Then,
> we assemble the resulting individual regexp into valid blocks.
>
> This raises a very significant performance win for large
> `.hgignore file`:
>
> Before: ! wall 0.153153 comb 0.150000 user 0.150000 sys 0.000000
> (median of 66)
> After: ! wall 0.059793 comb 0.060000 user 0.060000 sys 0.000000
> (median of 100)
>
> diff --git a/mercurial/match.py b/mercurial/match.py
> --- a/mercurial/match.py
> +++ b/mercurial/match.py
> @@ -1185,6 +1185,7 @@ def _buildmatch(kindpats, globsuffix, li
> return regex, lambda f: any(mf(f) for mf in matchfuncs)
>
> MAX_RE_SIZE = 20000
> +_BASE_SIZE = len('(?:)') - 1
>
>
> I think I asked before why MAX_RE_SIZE is "public" and _BASE_SIZE is
> "private".
MAX_RE_SIZE is a limit that impacts the external world (since RE larger
than 20 000 are rejected). The other one is a pure implementation detail.
I don't feel strongly about it and I'm fine aligning them one way or
another if you feel like it.
>
> Also, why do you subtract 1 from BASE_SIZE?
Because for N joined regexp there will be N-1 '|'. See lower for more
details
>
>
>
> def _joinregexes(regexps):
> """gather multiple regular expressions into a single one"""
> @@ -1203,20 +1204,31 @@ def _buildregexmatch(kindpats, globsuffi
> OverflowError
> """
> try:
> - regex = _joinregexes([_regex(k, p, globsuffix)
> - for (k, p, s) in kindpats])
> - if len(regex) <= MAX_RE_SIZE:
> - return regex, _rematcher(regex)
> - # We're using a Python with a tiny regex engine and we
> - # made it explode, so we'll divide the pattern list in two
> - # until it works
> - l = len(kindpats)
> - if l < 2:
> - # TODO: raise error.Abort here
> - raise OverflowError
> - regexa, a = _buildregexmatch(kindpats[:l//2], globsuffix)
> - regexb, b = _buildregexmatch(kindpats[l//2:], globsuffix)
> - return regex, lambda s: a(s) or b(s)
> + allgroups = []
> + regexps = [_regex(k, p, globsuffix) for (k, p, s) in
> kindpats]
> + fullregexp = _joinregexes(regexps)
> +
> + startidx = 0
> + groupsize = _BASE_SIZE
> + for idx, r in enumerate(regexps):
> + piecesize = len(r)
>
>
> This size is excluding the unnamed group wrapping, right? (I'm not
> asking for a change here, just as context for later questions.)
Yes, this is the pure size of the regexps produced by `_regex`.
>
> + if (piecesize + 4) > MAX_RE_SIZE:
>
>
> What's this 4? I think it's for the unnamed group wrapping, i.e.
> (BASE_SIZE + 1). Use that?
Yes, another way to do this would be to avoid the `-1` on _BASE_SIZE and
applying it explicitly in the `groupsize = _BASE_SIZE` lines (`groupsize
= _BASE_SIZE + 1`)
>
>
> + raise OverflowError
> + elif (groupsize + 1 + piecesize) > MAX_RE_SIZE:
> + group = regexps[startidx:idx]
> + allgroups.append(_joinregexes(group))
> + startidx = idx
> + groupsize = _BASE_SIZE
> + groupsize += piecesize + 1
>
>
> I suppose the "1" is for the "|"-separator. Shouldn't we add
> (BASE_SIZE + 1) here too
The 1 is for the |. we must not add _BASE_SIZE since there is only a
single external grouping all joined regexp. _BASE_SIZE added once for
each group.
> (and maybe redefine BASE_SIZE to include the additional 1)? Perhaps the
Sentence seems to have been cut.
>
> Would it be correct to initialize groupsize to 0 and add
This sentence seems to have been cut too.
>
> +
> + if startidx == 0:
> + func = _rematcher(fullregexp)
> + else:
> + group = regexps[startidx:]
> + allgroups.append(_joinregexes(group))
> + allmatchers = [_rematcher(g) for g in allgroups]
> + func = lambda s: any(m(s) for m in allmatchers)
> + return fullregexp, func
> except re.error:
> for k, p, s in kindpats:
> try:
>
>
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