From patchwork Sat Sep 24 19:37:18 2016
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Subject: [3,of,4] revlog: add instance variable controlling delta chain use
From: Gregory Szorc <gregory.szorc@gmail.com>
X-Patchwork-Id: 16781
Message-Id: <712281c3ab4b6e6e8ae1.1474745838@ubuntu-vm-main>
To: mercurial-devel@mercurial-scm.org
Date: Sat, 24 Sep 2016 12:37:18 -0700

# HG changeset patch
# User Gregory Szorc <gregory.szorc@gmail.com>
# Date 1474745137 25200
#      Sat Sep 24 12:25:37 2016 -0700
# Node ID 712281c3ab4b6e6e8ae109fa0673d4d6321d82fd
# Parent  af899e2937e1a8058e82e3eaf6b2160f6cf98fa9
revlog: add instance variable controlling delta chain use

This is to support disabling delta chains on the changelog in a
subsequent patch.

diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -292,16 +292,18 @@ class revlog(object):
                               % (self.indexfile, flags >> 16))
         elif fmt == REVLOGNG and flags & ~REVLOGNG_FLAGS:
             raise RevlogError(_("index %s unknown flags %#04x for revlogng")
                               % (self.indexfile, flags >> 16))
         elif fmt > REVLOGNG:
             raise RevlogError(_("index %s unknown format %d")
                               % (self.indexfile, fmt))
 
+        self._storedeltachains = True
+
         self._io = revlogio()
         if self.version == REVLOGV0:
             self._io = revlogoldio()
         try:
             d = self._io.parseindex(indexdata, self._inline)
         except (ValueError, IndexError):
             raise RevlogError(_("index %s is corrupted") % (self.indexfile))
         self.index, nodemap, self._chunkcache = d
@@ -1463,17 +1465,17 @@ class revlog(object):
         # become comparable to the uncompressed text
         if text is None:
             textlen = mdiff.patchedsize(self.rawsize(cachedelta[0]),
                                         cachedelta[1])
         else:
             textlen = len(text)
 
         # should we try to build a delta?
-        if prev != nullrev:
+        if prev != nullrev and self._storedeltachains:
             tested = set()
             if cachedelta and self._generaldelta and self._lazydeltabase:
                 # Assume what we received from the server is a good choice
                 # build delta will reuse the cache
                 candidatedelta = builddelta(cachedelta[0])
                 tested.add(cachedelta[0])
                 if self._isgooddelta(candidatedelta, textlen):
                     delta = candidatedelta