Disabling the change cache by default.

Since the change cache can mess-up multi-server setups,
it is now disabled by default.

Change-Id: Ia8dc83f675bbfc1f6467cfed29a964554e2b1951

Documentation/config-gerrit.txt

@@ -478,11 +478,15 @@ the first request into the second to ensure it can complete.
 
 cache `"changes"`::
 +
-Each item caches all changes tied to one project. Default size
-is 1024, which means all changes for up to 1024 projects can be held
-in the cache. This cache should probably be disabled in a multi-master
-setup where change updates are not communicated between servers. The
-cache should be flushed whenever the database changes table is modified
+The size determines the number of projects that will have all its changes
+cached. If the cache is set to 1024, this means all changes for up to
+1024 projects can be held in the cache.
++
+Default size is 0 (disabled). It is disabled by default due to the fact
+that change updates are not communicated between Gerrit servers.
+Hence this cache should be disabled in an multi-master/multi-slave setup.
++
+The cache should be flushed whenever the database changes table is modified
 outside of gerrit.
 
 cache `"diff"`::

gerrit-server/src/main/java/com/google/gerrit/server/git/ChangeCache.java

@@ -48,7 +48,7 @@ public class ChangeCache implements GitReferenceUpdatedListener {
         cache(ID_CACHE,
             Project.NameKey.class,
             new TypeLiteral<List<Change>>() {})
-          .maximumWeight(1024)
+          .maximumWeight(0)
           .loader(Loader.class);
       }
     };