From patchwork Fri Dec 13 23:58:04 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: D7665: dirstate: when calling rebuild(), avoid some N^2 codepaths From: phabricator X-Patchwork-Id: 43830 Message-Id: To: Phabricator Cc: mercurial-devel@mercurial-scm.org Date: Fri, 13 Dec 2019 23:58:04 +0000 spectral created this revision. Herald added a subscriber: mercurial-devel. Herald added a reviewer: hg-reviewers. REVISION SUMMARY I had a user repo with 200k files in it. Calling `hg debugrebuilddirstate` took tens of minutes (I didn't wait for it). In that situation, changedfiles==allfiles, and both are lists. This meant that we had to run an average of 100k comparisons, for each of 200k files, just to check whether a file needed to have normallookup called (it always did), or drop. While it's probably not a huge issue, in my very awkward synthetic benchmark I wrote (not using a benchmark library or anything), I was seeing some slowdowns for small-changedfiles and very-large-allfiles invocations, with an inflection somewhere around 10 items in changedfiles (regardless of the size of allfiles); above 10 items in changedfiles, the new code appears to always be faster. For the case of 50k files in changedfiles and the same items in allfiles, I'm seeing differences of 15s of just running comparisons vs. 0.003793s. I haven't bothered to run a comparison of 200k items in changedfiles and allfiles. :) REPOSITORY rHG Mercurial BRANCH default REVISION DETAIL https://phab.mercurial-scm.org/D7665 AFFECTED FILES mercurial/dirstate.py CHANGE DETAILS To: spectral, #hg-reviewers Cc: mercurial-devel diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py --- a/mercurial/dirstate.py +++ b/mercurial/dirstate.py @@ -603,19 +603,34 @@ def rebuild(self, parent, allfiles, changedfiles=None): if changedfiles is None: # Rebuild entire dirstate - changedfiles = allfiles + to_lookup = allfiles + to_drop = [] lastnormaltime = self._lastnormaltime self.clear() self._lastnormaltime = lastnormaltime + elif len(changedfiles) < 10: + # Avoid turning allfiles into a set, which can be expensive if it's + # large. + to_lookup = [] + to_drop = [] + for f in changedfiles: + if f in allfiles: + to_lookup.append(f) + else: + to_drop.append(f) + else: + changedfilesset = set(changedfiles) + to_lookup = changedfilesset.intersection(set(allfiles)) + to_drop = changedfilesset - to_lookup if self._origpl is None: self._origpl = self._pl self._map.setparents(parent, nullid) - for f in changedfiles: - if f in allfiles: - self.normallookup(f) - else: - self.drop(f) + + for f in to_lookup: + self.normallookup(f) + for f in to_drop: + self.drop(f) self._dirty = True