Rewrite ChangeRebuilder to better use NoteDbUpdateManager

Let's give up on the idea for now of reusing a single update manager
across multiple changes. With the common case of a FileRepository,
opening the repository is cheap (it's probably held open in the cache)
and writing out disjoint sets of loose objects and refs doesn't
benefit from batching them together. On googlesource.com's DFS
backend, we will be handling aggregation using custom code anyway.

However, we can now use the ChainedReceiveCommands exposed by
NoteDbUpdateManager to batch together updates to a single ref, in
particular the delete of the old value and the add of the new value.

Change-Id: I2f2c471856d803e5986853144afd76b375b314b0

gerrit-pgm/src/main/java/com/google/gerrit/pgm/RebuildNotedb.java

@@ -108,44 +108,43 @@ public class RebuildNotedb extends SiteProgram {
     System.out.println("Rebuilding the notedb");
     ChangeRebuilder rebuilder = sysInjector.getInstance(ChangeRebuilder.class);
 
-    Multimap<Project.NameKey, Change> changesByProject = getChangesByProject();
-    final AtomicBoolean ok = new AtomicBoolean(true);
+    Multimap<Project.NameKey, Change.Id> changesByProject =
+        getChangesByProject();
+    AtomicBoolean ok = new AtomicBoolean(true);
     Stopwatch sw = Stopwatch.createStarted();
     GitRepositoryManager repoManager =
         sysInjector.getInstance(GitRepositoryManager.class);
-    final Project.NameKey allUsersName =
+    Project.NameKey allUsersName =
         sysInjector.getInstance(AllUsersName.class);
     try (Repository allUsersRepo =
         repoManager.openMetadataRepository(allUsersName)) {
       deleteRefs(RefNames.REFS_DRAFT_COMMENTS, allUsersRepo);
       deleteRefs(RefNames.REFS_STARRED_CHANGES, allUsersRepo);
-      for (final Project.NameKey project : changesByProject.keySet()) {
-        try (Repository repo = repoManager.openMetadataRepository(project)) {
+      for (Project.NameKey project : changesByProject.keySet()) {
+        try {
           List<ListenableFuture<?>> futures = Lists.newArrayList();
 
           // Here, we elide the project name to 50 characters to ensure that
           // the whole monitor line for a project fits on one line (<80 chars).
           final MultiProgressMonitor mpm = new MultiProgressMonitor(System.out,
               FormatUtil.elide(project.get(), 50));
-          final Task doneTask =
+          Task doneTask =
               mpm.beginSubTask("done", changesByProject.get(project).size());
-          final Task failedTask =
+          Task failedTask =
               mpm.beginSubTask("failed", MultiProgressMonitor.UNKNOWN);
 
-          for (final Change c : changesByProject.get(project)) {
-            final ListenableFuture<?> future =
-                rebuilder.rebuildAsync(c, executor, repo);
+          for (Change.Id id : changesByProject.get(project)) {
+            ListenableFuture<?> future = rebuilder.rebuildAsync(id, executor);
             futures.add(future);
             future.addListener(
-                new RebuildListener(c.getId(), future, ok, doneTask, failedTask),
+                new RebuildListener(id, future, ok, doneTask, failedTask),
                 MoreExecutors.directExecutor());
           }
 
           mpm.waitFor(Futures.transformAsync(Futures.successfulAsList(futures),
               new AsyncFunction<List<?>, Void>() {
-                  @Override
-                public ListenableFuture<Void> apply(List<?> input)
-                    throws Exception {
+                @Override
+                public ListenableFuture<Void> apply(List<?> input) {
                   mpm.end();
                   return Futures.immediateFuture(null);
                 }
@@ -213,17 +212,17 @@ public class RebuildNotedb extends SiteProgram {
     }
   }
 
-  private Multimap<Project.NameKey, Change> getChangesByProject()
+  private Multimap<Project.NameKey, Change.Id> getChangesByProject()
       throws OrmException {
     // Memorize all changes so we can close the db connection and allow
     // rebuilder threads to use the full connection pool.
     SchemaFactory<ReviewDb> schemaFactory = sysInjector.getInstance(Key.get(
         new TypeLiteral<SchemaFactory<ReviewDb>>() {}));
-    Multimap<Project.NameKey, Change> changesByProject =
+    Multimap<Project.NameKey, Change.Id> changesByProject =
         ArrayListMultimap.create();
     try (ReviewDb db = schemaFactory.open()) {
       for (Change c : db.changes().all()) {
-        changesByProject.put(c.getProject(), c);
+        changesByProject.put(c.getProject(), c.getId());
       }
       return changesByProject;
     }

gerrit-server/src/main/java/com/google/gerrit/server/notedb/ChangeRebuilder.java

@@ -43,18 +43,18 @@ import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.PatchLineCommentsUtil;
 import com.google.gerrit.server.git.ChainedReceiveCommands;
+import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.patch.PatchListCache;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.gerrit.server.project.NoSuchChangeException;
 import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.SchemaFactory;
 import com.google.inject.Inject;
-import com.google.inject.Provider;
+import com.google.inject.util.Providers;
 
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectInserter;
-import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.RefUpdate;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevWalk;
@@ -77,7 +77,8 @@ public class ChangeRebuilder {
   private static final long TS_WINDOW_MS =
       TimeUnit.MILLISECONDS.convert(1, TimeUnit.SECONDS);
 
-  private final Provider<ReviewDb> dbProvider;
+  private final SchemaFactory<ReviewDb> schemaFactory;
+  private final GitRepositoryManager repoManager;
   private final ChangeControl.GenericFactory controlFactory;
   private final IdentifiedUser.GenericFactory userFactory;
   private final PatchListCache patchListCache;
@@ -86,14 +87,16 @@ public class ChangeRebuilder {
   private final NoteDbUpdateManager.Factory updateManagerFactory;
 
   @Inject
-  ChangeRebuilder(Provider<ReviewDb> dbProvider,
+  ChangeRebuilder(SchemaFactory<ReviewDb> schemaFactory,
+      GitRepositoryManager repoManager,
       ChangeControl.GenericFactory controlFactory,
       IdentifiedUser.GenericFactory userFactory,
       PatchListCache patchListCache,
       ChangeUpdate.Factory updateFactory,
       ChangeDraftUpdate.Factory draftUpdateFactory,
       NoteDbUpdateManager.Factory updateManagerFactory) {
-    this.dbProvider = dbProvider;
+    this.schemaFactory = schemaFactory;
+    this.repoManager = repoManager;
     this.controlFactory = controlFactory;
     this.userFactory = userFactory;
     this.patchListCache = patchListCache;
@@ -102,34 +105,44 @@ public class ChangeRebuilder {
     this.updateManagerFactory = updateManagerFactory;
   }
 
-  public ListenableFuture<?> rebuildAsync(final Change change,
-      ListeningExecutorService executor, final Repository changeRepo) {
+  public ListenableFuture<?> rebuildAsync(final Change.Id id,
+      ListeningExecutorService executor) {
     return executor.submit(new Callable<Void>() {
         @Override
       public Void call() throws Exception {
-        rebuild(change, changeRepo);
+        try (ReviewDb db = schemaFactory.open()) {
+          rebuild(db, id);
+        }
         return null;
       }
     });
   }
 
-  public void rebuild(Change change, Repository changeRepo)
+  public void rebuild(ReviewDb db, Change.Id changeId)
       throws NoSuchChangeException, IOException, OrmException {
-    ReviewDb db = dbProvider.get();
-    Change.Id changeId = change.getId();
+    Change change = db.changes().get(changeId);
+    if (change == null) {
+      return;
+    }
+    NoteDbUpdateManager manager =
+        updateManagerFactory.create(change.getProject());
+
     // We will rebuild all events, except for draft comments, in buckets based
     // on author and timestamp.
     List<Event> events = Lists.newArrayList();
     Multimap<Account.Id, PatchLineCommentEvent> draftCommentEvents =
         ArrayListMultimap.create();
 
-    try (RevWalk rw = new RevWalk(changeRepo)) {
-      events.addAll(getHashtagsEvents(change, changeRepo, rw));
+    Repository changeMetaRepo = manager.getChangeRepo();
+    events.addAll(getHashtagsEvents(change, manager));
 
-      deleteRef(change, changeRepo);
+    // Delete ref only after hashtags have been read
+    deleteRef(change, changeMetaRepo, manager.getChangeCommands());
 
+    try (Repository codeRepo = repoManager.openRepository(change.getProject());
+        RevWalk codeRw = new RevWalk(codeRepo)) {
       for (PatchSet ps : db.patchSets().byChange(changeId)) {
-        events.add(new PatchSetEvent(change, ps, rw));
+        events.add(new PatchSetEvent(change, ps, codeRw));
         for (PatchLineComment c : db.patchComments().byPatchSet(ps.getId())) {
           PatchLineCommentEvent e =
               new PatchLineCommentEvent(c, change, ps, patchListCache);
@@ -153,16 +166,13 @@ public class ChangeRebuilder {
 
     Collections.sort(events);
     events.add(new FinalUpdatesEvent(change, notedbChange));
-    // TODO(dborowitz): share manager across changes.
-    NoteDbUpdateManager manager =
-        updateManagerFactory.create(change.getProject());
     ChangeUpdate update = null;
     for (Event e : events) {
       if (!sameUpdate(e, update)) {
         if (update != null) {
           manager.add(update);
         }
-        IdentifiedUser user = userFactory.create(dbProvider, e.who);
+        IdentifiedUser user = userFactory.create(Providers.of(db), e.who);
         update = updateFactory.create(
             controlFactory.controlFor(db, change, user), e.when);
         update.setPatchSetId(e.psId);
@@ -172,7 +182,7 @@ public class ChangeRebuilder {
     manager.add(update);
 
     for (Account.Id author : draftCommentEvents.keys()) {
-      IdentifiedUser user = userFactory.create(dbProvider, author);
+      IdentifiedUser user = userFactory.create(Providers.of(db), author);
       ChangeDraftUpdate draftUpdate = null;
       for (PatchLineCommentEvent e : draftCommentEvents.get(author)) {
         if (!sameUpdate(e, draftUpdate)) {
@@ -188,17 +198,16 @@ public class ChangeRebuilder {
       manager.add(draftUpdate);
     }
 
-    createStarredChangesRefs(changeId, manager.getAllUsersCommands(),
+    createStarredChangesRefs(db, changeId, manager.getAllUsersCommands(),
         manager.getAllUsersRepo());
     manager.execute();
   }
 
-  private void createStarredChangesRefs(Change.Id changeId,
+  private void createStarredChangesRefs(ReviewDb db, Change.Id changeId,
       ChainedReceiveCommands allUsersCmds, Repository allUsersRepo)
           throws IOException, OrmException {
     ObjectId emptyTree = emptyTree(allUsersRepo);
-    for (StarredChange starred : dbProvider.get().starredChanges()
-        .byChange(changeId)) {
+    for (StarredChange starred : db.starredChanges().byChange(changeId)) {
       allUsersCmds.add(new ReceiveCommand(ObjectId.zeroId(), emptyTree,
           RefNames.refsStarredChanges(starred.getAccountId(), changeId)));
     }
@@ -213,16 +222,18 @@ public class ChangeRebuilder {
   }
 
   private List<HashtagsEvent> getHashtagsEvents(Change change,
-      Repository changeRepo, RevWalk rw) throws IOException {
+      NoteDbUpdateManager manager) throws IOException {
     String refName = ChangeNoteUtil.changeRefName(change.getId());
-    Ref ref = changeRepo.exactRef(refName);
-    if (ref == null) {
+    ObjectId old = manager.getChangeCommands()
+        .getObjectId(manager.getChangeRepo(), refName);
+    if (old == null) {
       return Collections.emptyList();
     }
 
+    RevWalk rw = manager.getChangeRevWalk();
     List<HashtagsEvent> events = new ArrayList<>();
     rw.reset();
-    rw.markStart(rw.parseCommit(ref.getObjectId()));
+    rw.markStart(rw.parseCommit(old));
     for (RevCommit commit : rw) {
       Account.Id authorId =
           ChangeNoteUtil.parseIdent(commit.getAuthorIdent());
@@ -264,28 +275,11 @@ public class ChangeRebuilder {
     return new PatchSet.Id(change.getId(), psId);
   }
 
-  private void deleteRef(Change change, Repository changeRepo)
-      throws IOException {
+  private void deleteRef(Change change, Repository repo,
+      ChainedReceiveCommands cmds) throws IOException {
     String refName = ChangeNoteUtil.changeRefName(change.getId());
-    RefUpdate ru = changeRepo.updateRef(refName, true);
-    ru.setForceUpdate(true);
-    RefUpdate.Result result = ru.delete();
-    switch (result) {
-      case FORCED:
-      case NEW:
-      case NO_CHANGE:
-        break;
-      case FAST_FORWARD:
-      case IO_FAILURE:
-      case LOCK_FAILURE:
-      case NOT_ATTEMPTED:
-      case REJECTED:
-      case REJECTED_CURRENT_BRANCH:
-      case RENAMED:
-      default:
-        throw new IOException(
-            String.format("Failed to delete ref %s: %s", refName, result));
-    }
+    ObjectId old = cmds.getObjectId(repo, refName);
+    cmds.add(new ReceiveCommand(old, ObjectId.zeroId(), refName));
   }
 
   private static long round(Date when) {

gerrit-server/src/main/java/com/google/gerrit/server/notedb/NoteDbUpdateManager.java

@@ -100,6 +100,21 @@ public class NoteDbUpdateManager {
     return this;
   }
 
+  Repository getChangeRepo() throws IOException {
+    initChangeRepo();
+    return changeRepo.repo;
+  }
+
+  RevWalk getChangeRevWalk() throws IOException {
+    initChangeRepo();
+    return changeRepo.rw;
+  }
+
+  ChainedReceiveCommands getChangeCommands() throws IOException {
+    initChangeRepo();
+    return changeRepo.cmds;
+  }
+
   public NoteDbUpdateManager setAllUsersRepo(Repository repo, RevWalk rw,
       ObjectInserter ins, ChainedReceiveCommands cmds) {
     checkState(allUsersRepo == null, "allUsers repo already initialized");