Merge lp:~thisfred/u1db/noop-shortcut into lp:u1db

[Eric Casteleijn]

Added shortcut so we make 2 fewer requests when we know there is nothing to sync

[Lucio Torre (lucio.torre)]

review: Approve

=== modified file 'src/u1db_sync_target.c'
--- src/u1db_sync_target.c	2012-05-15 09:03:31 +0000
+++ src/u1db_sync_target.c	2012-05-15 11:23:17 +0000
@@ -28,7 +28,7 @@
 static int st_record_sync_info(u1db_sync_target *st,
         const char *source_replica_uid, int source_gen);
 
-static int st_sync_exchange(u1db_sync_target *st, 
+static int st_sync_exchange(u1db_sync_target *st,
                           const char *source_replica_uid, int n_docs,
                           u1db_document **docs, int *generations,
                           int *target_gen, void *context,
@@ -566,11 +566,11 @@
     status = u1db_whats_changed(db, &local_gen, (void*)&to_send_state,
                                 whats_changed_to_doc_ids);
     if (status != U1DB_OK) { goto finish; }
-    // TODO: Shortcut when both sides know that they are at the same revision
-    //       eg:
-    //          if (local_gen == local_gen_known_by_target
-    //              && target_gen == target_gen_known_by_local)
-    //          { return U1DB_OK; }
+    if (local_gen == local_gen_known_by_target
+        && target_gen == target_gen_known_by_local)
+    {
+        return U1DB_OK;
+    }
     *local_gen_before_sync = local_gen;
     return_doc_state.db = db;
     return_doc_state.target_uid = target_uid;

=== modified file 'u1db/sync.py'
--- u1db/sync.py	2012-04-30 11:37:13 +0000
+++ u1db/sync.py	2012-05-15 11:23:17 +0000
@@ -95,15 +95,18 @@
          target_my_gen) = sync_target.get_sync_info(self.source._replica_uid)
         # what's changed since that generation and this current gen
         my_gen, changes = self.source.whats_changed(target_my_gen)
+
+        # this source last-seen database generation for the target
+        target_last_known_gen = self.source.get_sync_generation(
+            self.target_replica_uid)
+        if not changes and target_last_known_gen == target_gen:
+            return my_gen
         changed_doc_ids = [doc_id for doc_id, _ in changes]
         # prepare to send all the changed docs
         docs_to_send = self.source.get_docs(changed_doc_ids,
             check_for_conflicts=False)
         docs_by_generation = zip(docs_to_send, (gen for _, gen in changes))
 
-        # this source last-seen database generation for the target
-        target_last_known_gen = self.source.get_sync_generation(
-            self.target_replica_uid)
         # exchange documents and try to insert the returned ones with
         # the target, return target synced-up-to gen
         new_gen = sync_target.sync_exchange(docs_by_generation,
@@ -195,7 +198,8 @@
             'last_known_gen': self.source_last_known_generation
             })
         self._trace('before whats_changed')
-        gen, changes = self._db.whats_changed(self.source_last_known_generation)
+        gen, changes = self._db.whats_changed(
+            self.source_last_known_generation)
         self._trace('after whats_changed')
         self.new_gen = gen
         seen_ids = self.seen_ids

=== modified file 'u1db/tests/test_sync.py'
--- u1db/tests/test_sync.py	2012-05-09 16:09:04 +0000
+++ u1db/tests/test_sync.py	2012-05-15 11:23:17 +0000
@@ -647,6 +647,15 @@
         # original doc1 should have been removed from conflicts
         self.assertEqual(3, len(db3.get_doc_conflicts('the-doc')))
 
+    def test_sync_stops_after_get_sync_info(self):
+        self.db1.create_doc(tests.simple_doc)
+        self.sync(self.db1, self.db2)
+
+        def put_hook(state):
+            self.fail("Tracehook triggered for %s" % (state,))
+
+        self.sync(self.db1, self.db2, trace_hook=put_hook)
+
 
 class TestDbSync(tests.TestCaseWithServer):
     """Test db.sync remote sync shortcut"""