revset: improve roots revset performance
authorDurham Goode <durham@fb.com>
Mon, 31 Mar 2014 16:03:34 -0700
changeset 20895 f52e4ca93529
parent 20894 04e1596d5dbd
child 20896 9fae01831dea
revset: improve roots revset performance Previously we would iterate over every item in the subset, checking if it was in the provided args. This often meant iterating over every rev in the repo. Now we iterate over the args provided, checking if they exist in the subset. On a large repo this brings setting phase boundaries (which use this revset roots(X:: - X::Y)) down from 0.8 seconds to 0.4 seconds. The "roots((tip~100::) - (tip~100::tip))" revset in revsetbenchmarks shows it going from 0.12s to 0.10s, so we should be able to catch regressions here in the future. This actually introduces a regression in 'roots(all())' (0.2s to 0.26s) since we're now using spansets, which are slightly slower to do containment checks on. I believe this trade off is worth it, since it makes the revset O(number of args) instead of O(size of repo).
mercurial/revset.py
--- a/mercurial/revset.py	Tue Mar 25 14:10:01 2014 -0700
+++ b/mercurial/revset.py	Mon Mar 31 16:03:34 2014 -0700
@@ -1480,8 +1480,8 @@
     """``roots(set)``
     Changesets in set with no parent changeset in set.
     """
-    s = getset(repo, baseset(repo.changelog), x).set()
-    subset = baseset([r for r in subset if r in s])
+    s = getset(repo, spanset(repo), x).set()
+    subset = baseset([r for r in s if r in subset.set()])
     cs = _children(repo, subset, s)
     return subset - cs