Fix RepoRefCache stale checks during NoteDb rebuild

When rebuilding NoteDb meta-data from ReviewDb we are
actually mutating the /meta ref during a reindexing
operation.

This is an edge case that happens only once during
the on-line NoteDb upgrade and the trial mode.

Adapt the RepoRefCache use during NoteDb reindexing
and manage the situation where a staleness check
applies to a ref that has disappeared on disk.

Bug: Issue 15961
Release-Notes: skip
Change-Id: Iac642eb7a9b24882a0c77dbaee24853fb0b29827

2 files changed, 10 insertions, 5 deletions

diff --git a/java/com/google/gerrit/server/git/RepoRefCache.java b/java/com/google/gerrit/server/git/RepoRefCache.java
index c813b8375b..4fa33118f5 100644
--- a/java/com/google/gerrit/server/git/RepoRefCache.java
+++ b/java/com/google/gerrit/server/git/RepoRefCache.java
@@ -136,8 +136,9 @@ public class RepoRefCache implements RefCache {
     }
 
     try {
-      ObjectId diskId = refdb.exactRef(refName).getObjectId();
-      boolean isStale = !Optional.ofNullable(diskId).equals(id);
+      Optional<ObjectId> diskId =
+          Optional.ofNullable(refdb.exactRef(refName)).map(Ref::getObjectId);
+      boolean isStale = !diskId.equals(id);
       if (isStale) {
         log.atSevere().log(
             "Repository "
diff --git a/java/com/google/gerrit/server/notedb/ChangeNotes.java b/java/com/google/gerrit/server/notedb/ChangeNotes.java
index 3bceeeecda..e1f415d331 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNotes.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNotes.java
@@ -763,15 +763,19 @@ public class ChangeNotes extends AbstractChangeNotes<ChangeNotes> {
         refs = newRefCache;
       }
 
+      boolean changeUpToDate = true;
       try {
-        if (!NoteDbChangeState.isChangeUpToDate(state, refs, getChangeId())) {
-          return rebuildAndOpen(repo, id);
-        }
+        changeUpToDate = NoteDbChangeState.isChangeUpToDate(state, refs, getChangeId());
       } finally {
         if (newRefCache != null) {
+          // RepoRefCache needs to be closed for preventing caching before
+          // any potential mutation happens with rebuildAndOpen()
           newRefCache.close();
         }
       }
+      if (!changeUpToDate) {
+        return rebuildAndOpen(repo, id);
+      }
     }
     return super.openHandle(repo);
   }