changeset 46360:1726a53a8494

reverse-branch-cache: switch to doubling allocating scheme In preperation for updating the reverse-branch-cache incrementally whenever a new changeset comes in, avoid bad performance on resize with Python 3.7 (and likely other 3.x versions). Differential Revision: https://phab.mercurial-scm.org/D9778
author Joerg Sonnenberger <joerg@bec.de>
date Fri, 15 Jan 2021 01:20:47 +0100
parents 0600e8467101
children dfca84970da8
files mercurial/branchmap.py
diffstat 1 files changed, 10 insertions(+), 5 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/branchmap.py	Sun Jan 17 23:21:33 2021 +0100
+++ b/mercurial/branchmap.py	Fri Jan 15 01:20:47 2021 +0100
@@ -566,6 +566,7 @@
 # [4 byte hash prefix][4 byte branch name number with sign bit indicating open]
 _rbcrecfmt = b'>4sI'
 _rbcrecsize = calcsize(_rbcrecfmt)
+_rbcmininc = 64 * _rbcrecsize
 _rbcnodelen = 4
 _rbcbranchidxmask = 0x7FFFFFFF
 _rbccloseflag = 0x80000000
@@ -730,11 +731,15 @@
         if rev == nullrev:
             return
         rbcrevidx = rev * _rbcrecsize
-        if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
-            self._rbcrevs.extend(
-                b'\0'
-                * (len(self._repo.changelog) * _rbcrecsize - len(self._rbcrevs))
-            )
+        requiredsize = rbcrevidx + _rbcrecsize
+        rbccur = len(self._rbcrevs)
+        if rbccur < requiredsize:
+            # bytearray doesn't allocate extra space at least in Python 3.7.
+            # When multiple changesets are added in a row, precise resize would
+            # result in quadratic complexity. Overallocate to compensate by
+            # use the classic doubling technique for dynamic arrays instead.
+            # If there was a gap in the map before, less space will be reserved.
+            self._rbcrevs.extend(b'\0' * max(_rbcmininc, requiredsize))
         pack_into(_rbcrecfmt, self._rbcrevs, rbcrevidx, node, branchidx)
         self._rbcrevslen = min(self._rbcrevslen, rev)