emitrevision: if we need to compute a delta on the fly, try p1 or p2 first stable
authorPierre-Yves David <pierre-yves.david@octobus.net>
Thu, 24 Nov 2022 04:04:19 +0100
branchstable
changeset 49788 31b4675ca998
parent 49787 bb2c663c840f
child 49789 df750b81272f
emitrevision: if we need to compute a delta on the fly, try p1 or p2 first Falling back to `prev` does not yield any real value on modern storage and result in pathological changes to be created on the other side. Doing a delta against a parent will likely be smaller (helping the network) and will be safer to apply on the client (helping future pulls by Triggering intermediate snapshop where they will be needed by later deltas).
mercurial/utils/storageutil.py
--- a/mercurial/utils/storageutil.py	Mon Nov 28 16:27:23 2022 +0100
+++ b/mercurial/utils/storageutil.py	Thu Nov 24 04:04:19 2022 +0100
@@ -436,10 +436,21 @@
             # No guarantee the receiver has the delta parent, or Storage has a
             # fulltext revision.
             #
-            # Send delta against last revision (if possible), which in the
-            # common case should be similar enough to this revision that the
-            # delta is reasonable.
-            if prevrev is not None:
+            # We compute a delta on the fly to send over the wire.
+            #
+            # We start with a try against p1, which in the common case should
+            # be close to this revision content.
+            #
+            # note: we could optimize between p1 and p2 in merges cases.
+            if is_usable_base(p1rev):
+                baserev = p1rev
+            # if p1 was not an option, try p2
+            elif is_usable_base(p2rev):
+                baserev = p2rev
+            # Send delta against prev in despair
+            #
+            # using the closest available ancestors first might be better?
+            elif prevrev is not None:
                 baserev = prevrev
             else:
                 baserev = nullrev