Avoid re-reading refs in schema 161

A ref lookup using its name can be slow, especially in an unrepacked
NFS based repository. Instead, use a Ref object which is already
available to read labels.

Change-Id: I31bafad54b7f69059235cc466d4a3d732ba44d97

2 files changed, 17 insertions, 12 deletions

diff --git a/java/com/google/gerrit/server/StarredChangesUtil.java b/java/com/google/gerrit/server/StarredChangesUtil.java
index 9962c39153..035b3a5a1b 100644
--- a/java/com/google/gerrit/server/StarredChangesUtil.java
+++ b/java/com/google/gerrit/server/StarredChangesUtil.java
@@ -385,18 +385,23 @@ public class StarredChangesUtil {
   public static StarRef readLabels(Repository repo, String refName) throws IOException {
     try (TraceTimer traceTimer = TraceContext.newTimer("Read star labels from %s", refName)) {
       Ref ref = repo.exactRef(refName);
-      if (ref == null) {
-        return StarRef.MISSING;
-      }
+      return readLabels(repo, ref);
+    }
+  }
 
-      try (ObjectReader reader = repo.newObjectReader()) {
-        ObjectLoader obj = reader.open(ref.getObjectId(), Constants.OBJ_BLOB);
-        return StarRef.create(
-            ref,
-            Splitter.on(CharMatcher.whitespace())
-                .omitEmptyStrings()
-                .split(new String(obj.getCachedBytes(Integer.MAX_VALUE), UTF_8)));
-      }
+  public static StarRef readLabels(Repository repo, Ref ref) throws IOException {
+    if (ref == null) {
+      return StarRef.MISSING;
+    }
+    try (TraceTimer traceTimer =
+            TraceContext.newTimer("Read star labels from %s (without ref lookup)", ref.getName());
+        ObjectReader reader = repo.newObjectReader()) {
+      ObjectLoader obj = reader.open(ref.getObjectId(), Constants.OBJ_BLOB);
+      return StarRef.create(
+          ref,
+          Splitter.on(CharMatcher.whitespace())
+              .omitEmptyStrings()
+              .split(new String(obj.getCachedBytes(Integer.MAX_VALUE), UTF_8)));
     }
   }
 
diff --git a/java/com/google/gerrit/server/schema/Schema_161.java b/java/com/google/gerrit/server/schema/Schema_161.java
index 70010f830d..b84af60071 100644
--- a/java/com/google/gerrit/server/schema/Schema_161.java
+++ b/java/com/google/gerrit/server/schema/Schema_161.java
@@ -61,7 +61,7 @@ public class Schema_161 extends SchemaVersion {
       bru.setAllowNonFastForwards(true);
 
       for (Ref ref : git.getRefDatabase().getRefsByPrefix(RefNames.REFS_STARRED_CHANGES)) {
-        StarRef starRef = StarredChangesUtil.readLabels(git, ref.getName());
+        StarRef starRef = StarredChangesUtil.readLabels(git, ref);
 
         Set<Integer> mutedPatchSets =
             StarredChangesUtil.getStarredPatchSets(starRef.labels(), MUTE_LABEL);