Patchwork D10294: match: convert O(n) to O(log n) in exactmatcher.visitchildrenset

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Submitter phabricator
Date April 1, 2021, 7:21 p.m.
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Download mbox | patch
Permalink /patch/48610/
State Superseded
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phabricator - April 1, 2021, 7:21 p.m.
spectral created this revision.
Herald added a reviewer: hg-reviewers.
Herald added a subscriber: mercurial-patches.

  When using narrow, during rebase this is called (at least) once per directory in
  the set of files in the commit being rebased. Every time it's called, we did the
  set arithmetic (now extracted and cached), which was probably pretty cheap but
  not necessary to repeat each time, looped over every item in the matcher and
  kept things that started with the directory we were querying.
  With very large narrowspecs, and a commit that touched a file in a large number
  of directories, this was slow. In a pathological repo, the rebase of a single
  commit (that touched over 17k files, I believe in approximately as many
  directories) with a narrowspec that had >32k entries took 8,246s of profiled
  time, with 5,007s of that spent in visitchildrenset (transitively). With this
  change, the time spent in visitchildrenset is less than 34s (which is where my
  profile cut off). Most of the remaining time was network access due to our
  custom remotefilelog-based setup not properly prefetching.

  rHG Mercurial





To: spectral, #hg-reviewers
Cc: mercurial-patches, mercurial-devel


diff --git a/mercurial/ b/mercurial/
--- a/mercurial/
+++ b/mercurial/
@@ -7,6 +7,7 @@ 
 from __future__ import absolute_import, print_function
+import bisect
 import copy
 import itertools
 import os
@@ -798,14 +799,38 @@ 
     def visitdir(self, dir):
         return dir in self._dirs
+    @propertycache
+    def _visitchildrenset_candidates(self):
+        """A memoized set of candidates for visitchildrenset."""
+        return self._fileset | self._dirs - {b''}
+    @propertycache
+    def _sorted_visitchildrenset_candidates(self):
+        """A memoized sorted list of candidates for visitchildrenset."""
+        return sorted(self._visitchildrenset_candidates)
     def visitchildrenset(self, dir):
         if not self._fileset or dir not in self._dirs:
             return set()
-        candidates = self._fileset | self._dirs - {b''}
-        if dir != b'':
+        if dir == b'':
+            candidates = self._visitchildrenset_candidates
+        else:
+            candidates = self._sorted_visitchildrenset_candidates
             d = dir + b'/'
-            candidates = {c[len(d) :] for c in candidates if c.startswith(d)}
+            # Use bisect to find the first element potentially starting with d
+            # (i.e. >= d). This should always find at least one element (we'll
+            # assert later if this is not the case).
+            first = bisect.bisect_left(candidates, d)
+            # We need a representation of the first element that is > d that
+            # does not start with d, so since we added a `/` on the end of dir,
+            # we'll add whatever comes after slash (we could probably assume
+            # that `0` is after `/`, but let's not) to the end of dir instead.
+            dnext = dir + encoding.strtolocal(chr(ord(b'/') + 1))
+            # Use bisect to find the first element >= d_next
+            last = bisect.bisect_left(candidates, dnext, lo=first)
+            dlen = len(d)
+            candidates = {c[dlen :] for c in candidates[first:last]}
         # self._dirs includes all of the directories, recursively, so if
         # we're attempting to match foo/bar/baz.txt, it'll have '', 'foo',
         # 'foo/bar' in it. Thus we can safely ignore a candidate that has a