[git] Update references changed on the remote repo only

When repositories are synched, the backend needs to update
the local references to the ones set on the remote repository.
The backend processed all the references, including those
up to date. This made the synchronization very slow.

With this commit, only the references that were updated on
the remote repository will be modified locally. We have
improved the performance by 2. Repositories are in sync
two or more times than before.

Signed-off-by: Santiago Dueñas <[email protected]>

perceval/backends/core/git.py

@@ -1304,6 +1304,8 @@ def _update_references(self, refs):
             self._update_ref(old_ref, delete=True)
 
         # Update new references
+        current_refs = {ref.refname: ref.hash for ref in self._discover_refs()}
+
         for new_ref in refs:
             refname = new_ref.refname
 
@@ -1315,6 +1317,10 @@ def _update_references(self, refs):
                 logger.debug("Reference %s not needed; ignored for updating in sync process",
                              refname)
                 continue
+            elif refname in current_refs and new_ref.hash == current_refs[refname]:
+                logger.debug("Reference %s already up to date in sync process",
+                             refname)
+                continue
             else:
                 self._update_ref(new_ref)
 

releases/unreleased/git-sync-perfomance-improved.yml

@@ -0,0 +1,14 @@
+---
+title: Git sync improved for `--latest-items` flag
+category: performance
+author: Santiago Dueñas <[email protected]>
+issue: null
+notes: >
+  The speed updating a git repository when `--lates-items`
+  is set was very poor. The main problem was when the
+  references were updated to the new hashes. All the
+  active refs on the repository were modified, even when
+  they were up-to-date. Now, only references updated
+  on the remote repository are modified on the local one.
+  Repositories are synched 2 times faster than before.
+