diff mercurial/pure/parsers.py @ 44333:50ad851efd9b

nodemap: introduce append-only incremental update of the persistent data

Rewriting the full nodemap for each transaction has a cost we would like to
avoid. We introduce a new way to write persistent nodemap data by adding new
information at the end for file. Any new and updated block as added at the end
of the file. The last block is the new root node.

With this method, some of the block already on disk get "dereferenced" and
become dead data. In later changesets, We'll start tracking the amount of dead
data to eventually re-generate a full nodemap.

Differential Revision: https://phab.mercurial-scm.org/D7886

--- a/mercurial/pure/parsers.py	Wed Jan 15 15:49:45 2020 +0100
+++ b/mercurial/pure/parsers.py	Wed Jan 15 15:49:54 2020 +0100
@@ -156,13 +156,31 @@
         index."""
         return nodemaputil.persistent_data(self)
 
+    def nodemap_data_incremental(self):
+        """Return bytes containing a incremental update to persistent nodemap
+
+        This containst the data for an append-only update of the data provided
+        in the last call to `update_nodemap_data`.
+        """
+        if self._nm_root is None:
+            return None
+        data = nodemaputil.update_persistent_data(
+            self, self._nm_root, self._nm_max_idx, self._nm_rev
+        )
+        self._nm_root = self._nm_max_idx = self._nm_rev = None
+        return data
+
     def update_nodemap_data(self, nm_data):
         """provide full blokc of persisted binary data for a nodemap
 
         The data are expected to come from disk. See `nodemap_data_all` for a
         produceur of such data."""
         if nm_data is not None:
-            nodemaputil.parse_data(nm_data)
+            self._nm_root, self._nm_max_idx = nodemaputil.parse_data(nm_data)
+            if self._nm_root:
+                self._nm_rev = len(self) - 1
+            else:
+                self._nm_root = self._nm_max_idx = self._nm_rev = None
 
 
 class InlinedIndexObject(BaseIndexObject):