revlog: optimize _chunkraw when startrev==endrev
authorGregory Szorc <gregory.szorc@gmail.com>
Sun, 23 Oct 2016 10:40:33 -0700
changeset 30289 1f92056c4066
parent 30288 ceddc3d94d74
child 30290 1a0c1ad57833
revlog: optimize _chunkraw when startrev==endrev In many cases, _chunkraw() is called with startrev==endrev. When this is true, we can avoid an extra index lookup and some other minor operations. On the mozilla-unified repo, `hg perfrevlogchunks -c` says this has the following impact: ! read w/ reused fd ! wall 0.371846 comb 0.370000 user 0.350000 sys 0.020000 (best of 27) ! wall 0.337930 comb 0.330000 user 0.300000 sys 0.030000 (best of 30) ! read batch w/ reused fd ! wall 0.014952 comb 0.020000 user 0.000000 sys 0.020000 (best of 197) ! wall 0.014866 comb 0.010000 user 0.000000 sys 0.010000 (best of 196) So, we've gone from ~25x slower than batch to ~22.5x slower. At this point, there's probably not much else we can do except implement an optimized function in the index itself, including in C.
mercurial/revlog.py
--- a/mercurial/revlog.py	Sat Oct 22 15:41:23 2016 -0700
+++ b/mercurial/revlog.py	Sun Oct 23 10:40:33 2016 -0700
@@ -1113,9 +1113,12 @@
         # (functions are expensive).
         index = self.index
         istart = index[startrev]
-        iend = index[endrev]
         start = int(istart[0] >> 16)
-        end = int(iend[0] >> 16) + iend[1]
+        if startrev == endrev:
+            end = start + istart[1]
+        else:
+            iend = index[endrev]
+            end = int(iend[0] >> 16) + iend[1]
 
         if self._inline:
             start += (startrev + 1) * self._io.size