diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -481,7 +481,7 @@ class changelog(revlog.revlog):
             self._delaybuf = None
         self._divert = False
         # split when we're done
-        self._enforceinlinesize(tr)
+        self._enforceinlinesize(tr, side_write=False)
 
     def _writepending(self, tr):
         """create a file containing the unfinalized state for
@@ -512,9 +512,9 @@ class changelog(revlog.revlog):
 
         return False
 
-    def _enforceinlinesize(self, tr):
+    def _enforceinlinesize(self, tr, side_write=True):
         if not self._delayed:
-            revlog.revlog._enforceinlinesize(self, tr)
+            revlog.revlog._enforceinlinesize(self, tr, side_write=side_write)
 
     def read(self, nodeorrev):
         """Obtain data from a parsed changelog revision.
diff --git a/mercurial/filelog.py b/mercurial/filelog.py
--- a/mercurial/filelog.py
+++ b/mercurial/filelog.py
@@ -25,7 +25,7 @@ from .revlogutils import (
 
 @interfaceutil.implementer(repository.ifilestorage)
 class filelog:
-    def __init__(self, opener, path):
+    def __init__(self, opener, path, try_split=False):
         self._revlog = revlog.revlog(
             opener,
             # XXX should use the unencoded path
@@ -33,6 +33,7 @@ class filelog:
             radix=b'/'.join((b'data', path)),
             censorable=True,
             canonical_parent_order=False,  # see comment in revlog.py
+            try_split=try_split,
         )
         # Full name of the user visible file, relative to the repository root.
         # Used by LFS.
@@ -256,8 +257,8 @@ class filelog:
 class narrowfilelog(filelog):
     """Filelog variation to be used with narrow stores."""
 
-    def __init__(self, opener, path, narrowmatch):
-        super(narrowfilelog, self).__init__(opener, path)
+    def __init__(self, opener, path, narrowmatch, try_split=False):
+        super(narrowfilelog, self).__init__(opener, path, try_split=try_split)
         self._narrowmatch = narrowmatch
 
     def renamed(self, node):
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1240,7 +1240,12 @@ class revlogfilestorage:
         if path.startswith(b'/'):
             path = path[1:]
 
-        return filelog.filelog(self.svfs, path)
+        try_split = (
+            self.currenttransaction() is not None
+            or txnutil.mayhavepending(self.root)
+        )
+
+        return filelog.filelog(self.svfs, path, try_split=try_split)
 
 
 @interfaceutil.implementer(repository.ilocalrepositoryfilestorage)
@@ -1251,7 +1256,13 @@ class revlognarrowfilestorage:
         if path.startswith(b'/'):
             path = path[1:]
 
-        return filelog.narrowfilelog(self.svfs, path, self._storenarrowmatch)
+        try_split = (
+            self.currenttransaction() is not None
+            or txnutil.mayhavepending(self.root)
+        )
+        return filelog.narrowfilelog(
+            self.svfs, path, self._storenarrowmatch, try_split=try_split
+        )
 
 
 def makefilestorage(requirements, features, **kwargs):
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -302,6 +302,7 @@ class revlog:
         persistentnodemap=False,
         concurrencychecker=None,
         trypending=False,
+        try_split=False,
         canonical_parent_order=True,
     ):
         """
@@ -328,6 +329,7 @@ class revlog:
         self._nodemap_file = None
         self.postfix = postfix
         self._trypending = trypending
+        self._try_split = try_split
         self.opener = opener
         if persistentnodemap:
             self._nodemap_file = nodemaputil.get_nodemap_file(self)
@@ -511,6 +513,8 @@ class revlog:
             entry_point = b'%s.i.%s' % (self.radix, self.postfix)
         elif self._trypending and self.opener.exists(b'%s.i.a' % self.radix):
             entry_point = b'%s.i.a' % self.radix
+        elif self._try_split and self.opener.exists(b'%s.i.s' % self.radix):
+            entry_point = b'%s.i.s' % self.radix
         else:
             entry_point = b'%s.i' % self.radix
 
@@ -2015,7 +2019,7 @@ class revlog:
                 raise error.CensoredNodeError(self.display_id, node, text)
             raise
 
-    def _enforceinlinesize(self, tr):
+    def _enforceinlinesize(self, tr, side_write=True):
         """Check if the revlog is too big for inline and convert if so.
 
         This should be called after revisions are added to the revlog. If the
@@ -2032,7 +2036,8 @@ class revlog:
             raise error.RevlogError(
                 _(b"%s not found in the transaction") % self._indexfile
             )
-        trindex = None
+        if troffset:
+            tr.addbackup(self._indexfile, for_offset=True)
         tr.add(self._datafile, 0)
 
         existing_handles = False
@@ -2048,6 +2053,29 @@ class revlog:
             # No need to deal with sidedata writing handle as it is only
             # relevant with revlog-v2 which is never inline, not reaching
             # this code
+        if side_write:
+            old_index_file_path = self._indexfile
+            new_index_file_path = self._indexfile + b'.s'
+            opener = self.opener
+
+            fncache = getattr(opener, 'fncache', None)
+            if fncache is not None:
+                fncache.addignore(new_index_file_path)
+
+            # the "split" index replace the real index when the transaction is finalized
+            def finalize_callback(tr):
+                opener.rename(
+                    new_index_file_path,
+                    old_index_file_path,
+                    checkambig=True,
+                )
+
+            tr.registertmp(new_index_file_path)
+            if self.target[1] is not None:
+                finalize_id = b'000-revlog-split-%d-%s' % self.target
+            else:
+                finalize_id = b'000-revlog-split-%d' % self.target[0]
+            tr.addfinalize(finalize_id, finalize_callback)
 
         new_dfh = self._datafp(b'w+')
         new_dfh.truncate(0)  # drop any potentially existing data
@@ -2055,17 +2083,10 @@ class revlog:
             with self._indexfp() as read_ifh:
                 for r in self:
                     new_dfh.write(self._getsegmentforrevs(r, r, df=read_ifh)[1])
-                    if (
-                        trindex is None
-                        and troffset
-                        <= self.start(r) + r * self.index.entry_size
-                    ):
-                        trindex = r
                 new_dfh.flush()
 
-            if trindex is None:
-                trindex = 0
-
+            if side_write:
+                self._indexfile = new_index_file_path
             with self.__index_new_fp() as fp:
                 self._format_flags &= ~FLAG_INLINE_DATA
                 self._inline = False
@@ -2079,16 +2100,9 @@ class revlog:
                 if self._docket is not None:
                     self._docket.index_end = fp.tell()
 
-                # There is a small transactional race here. If the rename of
-                # the index fails, we should remove the datafile. It is more
-                # important to ensure that the data file is not truncated
-                # when the index is replaced as otherwise data is lost.
-                tr.replace(self._datafile, self.start(trindex))
-
-                # the temp file replace the real index when we exit the context
-                # manager
-
-            tr.replace(self._indexfile, trindex * self.index.entry_size)
+                # If we don't use side-write, the temp file replace the real
+                # index when we exit the context manager
+
             nodemaputil.setup_persistent_nodemap(tr, self)
             self._segmentfile = randomaccessfile.randomaccessfile(
                 self.opener,
diff --git a/tests/test-transaction-rollback-on-revlog-split.t b/tests/test-transaction-rollback-on-revlog-split.t
--- a/tests/test-transaction-rollback-on-revlog-split.t
+++ b/tests/test-transaction-rollback-on-revlog-split.t
@@ -9,12 +9,12 @@ Helper extension to intercept renames an
   > from mercurial import extensions, util
   > 
   > def extsetup(ui):
-  >     def close(orig, *args, **kwargs):
-  >         path = util.normpath(args[0]._atomictempfile__name)
-  >         if path.endswith(b'/.hg/store/data/file.i'):
+  >     def rename(orig, src, dest, *args, **kwargs):
+  >         path = util.normpath(dest)
+  >         if path.endswith(b'data/file.i'):
   >             os.kill(os.getpid(), signal.SIGKILL)
-  >         return orig(*args, **kwargs)
-  >     extensions.wrapfunction(util.atomictempfile, 'close', close)
+  >         return orig(src, dest, *args, **kwargs)
+  >     extensions.wrapfunction(util, 'rename', rename)
   > EOF
 
   $ cat > $TESTTMP/intercept_after_rename.py << EOF
@@ -30,6 +30,14 @@ Helper extension to intercept renames an
   >             os.kill(os.getpid(), signal.SIGKILL)
   >         return r
   >     extensions.wrapfunction(util.atomictempfile, 'close', close)
+  > def extsetup(ui):
+  >     def rename(orig, src, dest, *args, **kwargs):
+  >         path = util.normpath(dest)
+  >         r = orig(src, dest, *args, **kwargs)
+  >         if path.endswith(b'data/file.i'):
+  >             os.kill(os.getpid(), signal.SIGKILL)
+  >         return r
+  >     extensions.wrapfunction(util, 'rename', rename)
   > EOF
 
   $ cat > $TESTTMP/killme.py << EOF
@@ -75,7 +83,7 @@ setup a repository for tests
   $ printf '%20d' '1' > file
   $ hg commit -Aqmc
   $ dd if=/dev/zero of=file bs=1k count=128 > /dev/null 2>&1
-  $ hg commit -AqmD
+  $ hg commit -AqmD --traceback
 
 Reference size:
   $ f -s file
@@ -127,32 +135,33 @@ Reference size:
 #endif
 
 
-The revlog have been split on disk
+The inline revlog still exist, but a split version exist next to it
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
-  .hg/store/data/file.i: size=256
+  .hg/store/data/file.i: size=132395
+  .hg/store/data/file.i.s: size=256
 
-  $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file | tail -1
-  data/file.i 128
 
 The first file.i entry should match the "Reference size" above.
 The first file.d entry is the temporary record during the split,
 
-The second entry after the split happened. The sum of the second file.d
-and the second file.i entry should match the first file.i entry.
+A "temporary file" entry exist for the split index.
 
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file
   data/file.i 1174
   data/file.d 0
-  data/file.d 1046
-  data/file.i 128
+  $ cat .hg/store/journal.backupfiles | tr -s '\000' ' ' | tr -s '\00' ' '| grep data/file
+   data/file.i data/journal.backup.file.i 0
+   data/file.i.s 0
+
+recover is rolling the split back, the fncache is still valid
+
   $ hg recover
   rolling back interrupted transaction
   (verify step skipped, run `hg verify` to check your repository content)
   $ f -s .hg/store/data/file*
-  .hg/store/data/file.d: size=1046
-  .hg/store/data/file.i: size=128
+  .hg/store/data/file.i: size=1174
   $ hg tip
   changeset:   1:cfa8d6e60429
   tag:         tip
@@ -161,12 +170,8 @@ and the second file.i entry should match
   summary:     b
   
   $ hg verify -q
-   warning: revlog 'data/file.d' not in fncache!
-  1 warnings encountered!
-  hint: run "hg debugrebuildfncache" to recover from corrupt fncache
   $ hg debugrebuildfncache --only-data
-  adding data/file.d
-  1 items added, 0 removed from fncache
+  fncache already up to date
   $ hg verify -q
   $ cd ..
 
@@ -189,36 +194,43 @@ Reference size:
   $ cat > .hg/hgrc <<EOF
   > [extensions]
   > intercept_rename = $TESTTMP/intercept_before_rename.py
-  > [hooks]
-  > pretxnchangegroup = python:$TESTTMP/killme.py:killme
   > EOF
 #if chg
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
   [255]
 #else
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
   Killed
   [137]
 #endif
 
-The data file is created, but the revlog is still inline
+The inline revlog still exist, but a split version exist next to it
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
   .hg/store/data/file.i: size=132395
+  .hg/store/data/file.i.s: size=256
 
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file
   data/file.i 1174
   data/file.d 0
-  data/file.d 1046
+
+recover is rolling the split back, the fncache is still valid
 
   $ hg recover
   rolling back interrupted transaction
   (verify step skipped, run `hg verify` to check your repository content)
   $ f -s .hg/store/data/file*
-  .hg/store/data/file.d: size=1046
   .hg/store/data/file.i: size=1174
   $ hg tip
   changeset:   1:cfa8d6e60429
@@ -235,8 +247,6 @@ Test a hard crash right after the index 
 
 Now retry the procedure but intercept the rename of the index.
 
-Things get corrupted /o\
-
   $ hg clone --quiet --rev 1 troffset-computation troffset-computation-crash-after-rename
   $ cd troffset-computation-crash-after-rename
 
@@ -249,21 +259,27 @@ Reference size:
   $ cat > .hg/hgrc <<EOF
   > [extensions]
   > intercept_rename = $TESTTMP/intercept_after_rename.py
-  > [hooks]
-  > pretxnchangegroup = python:$TESTTMP/killme.py:killme
   > EOF
 #if chg
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
   [255]
 #else
   $ hg pull ../troffset-computation
   pulling from ../troffset-computation
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
   Killed
   [137]
 #endif
 
-the revlog has been split on disk
+The inline revlog was over written on disk
 
   $ f -s .hg/store/data/file*
   .hg/store/data/file.d: size=132139
@@ -272,16 +288,14 @@ the revlog has been split on disk
   $ cat .hg/store/journal | tr -s '\000' ' ' | grep data/file
   data/file.i 1174
   data/file.d 0
-  data/file.d 1046
+
+recover is rolling the split back, the fncache is still valid
 
   $ hg recover
   rolling back interrupted transaction
-  abort: attempted to truncate data/file.i to 1174 bytes, but it was already 256 bytes
-  
-  [255]
+  (verify step skipped, run `hg verify` to check your repository content)
   $ f -s .hg/store/data/file*
-  .hg/store/data/file.d: size=1046
-  .hg/store/data/file.i: size=256
+  .hg/store/data/file.i: size=1174
   $ hg tip
   changeset:   1:cfa8d6e60429
   tag:         tip
@@ -290,23 +304,6 @@ the revlog has been split on disk
   summary:     b
   
   $ hg verify -q
-  abandoned transaction found - run hg recover
-   warning: revlog 'data/file.d' not in fncache!
-   file@0: data length off by -131093 bytes
-   file@2: unpacking fa1120531cc1: partial read of revlog data/file.d; expected 21 bytes from offset 1046, got 0
-   file@3: unpacking a631378adaa3: partial read of revlog data/file.d; expected 131072 bytes from offset 1067, got -21
-   file@?: rev 2 points to nonexistent changeset 2
-   (expected )
-   file@?: fa1120531cc1 not in manifests
-   file@?: rev 3 points to nonexistent changeset 3
-   (expected )
-   file@?: a631378adaa3 not in manifests
-  not checking dirstate because of previous errors
-  3 warnings encountered!
-  hint: run "hg debugrebuildfncache" to recover from corrupt fncache
-  7 integrity errors encountered!
-  (first damaged changeset appears to be 0)
-  [1]
   $ cd ..
 
 Have the transaction rollback itself without any hard crash
@@ -332,11 +329,12 @@ Repeat the original test but let hg roll
   abort: pretxnchangegroup hook exited with status 1
   [40]
 
-File are still split on disk, with the expected size.
+The split was rollback
 
   $ f -s .hg/store/data/file*
-  .hg/store/data/file.d: size=1046
-  .hg/store/data/file.i: size=128
+  .hg/store/data/file.d: size=0
+  .hg/store/data/file.i: size=1174
+
 
   $ hg tip
   changeset:   1:cfa8d6e60429
@@ -346,9 +344,6 @@ File are still split on disk, with the e
   summary:     b
   
   $ hg verify -q
-   warning: revlog 'data/file.d' not in fncache!
-  1 warnings encountered!
-  hint: run "hg debugrebuildfncache" to recover from corrupt fncache
   $ cd ..
 
 Read race