Shard refs/draft-comments/* by change instead of account ID

The motivation is the same as in Ib81d462: scanning the whole
refs/draft-comments/* space (with grows without bound) when reindexing
a change is potentially too slow.

Instead of refs/draft-comments/<sharded account>/<change>, use
refs/draft-comments/<sharded change>/<account>. This is mostly
straightforward, since there are relatively few places that scan
multiple refs; most callers just use the helper method in RefNames.

Change-Id: I063e2c496751f637d968c89c1501743074fb9025

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/DeleteDraftPatchSetIT.java

@@ -191,7 +191,7 @@ public class DeleteDraftPatchSetIT extends AbstractDaemonTest {
   private Ref getDraftRef(TestAccount account, Change.Id changeId)
       throws Exception {
     try (Repository repo = repoManager.openRepository(allUsers)) {
-      return repo.exactRef(RefNames.refsDraftComments(account.id, changeId));
+      return repo.exactRef(RefNames.refsDraftComments(changeId, account.id));
     }
   }
 

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/notedb/ChangeRebuilderIT.java

@@ -289,14 +289,14 @@ public class ChangeRebuilderIT extends AbstractDaemonTest {
 
     putDraft(user, id, 1, "comment by user");
     ObjectId userDraftsId = getMetaRef(
-        allUsers, RefNames.refsDraftComments(user.getId(), id));
+        allUsers, RefNames.refsDraftComments(id, user.getId()));
     assertThat(unwrapDb().changes().get(id).getNoteDbState()).isEqualTo(
         changeMetaId.name()
         + "," + user.getId() + "=" + userDraftsId.name());
 
     putDraft(admin, id, 2, "comment by admin");
     ObjectId adminDraftsId = getMetaRef(
-        allUsers, RefNames.refsDraftComments(admin.getId(), id));
+        allUsers, RefNames.refsDraftComments(id, admin.getId()));
     assertThat(admin.getId().get()).isLessThan(user.getId().get());
     assertThat(unwrapDb().changes().get(id).getNoteDbState()).isEqualTo(
         changeMetaId.name()
@@ -305,7 +305,7 @@ public class ChangeRebuilderIT extends AbstractDaemonTest {
 
     putDraft(admin, id, 2, "revised comment by admin");
     adminDraftsId = getMetaRef(
-        allUsers, RefNames.refsDraftComments(admin.getId(), id));
+        allUsers, RefNames.refsDraftComments(id, admin.getId()));
     assertThat(unwrapDb().changes().get(id).getNoteDbState()).isEqualTo(
         changeMetaId.name()
         + "," + admin.getId() + "=" + adminDraftsId.name()

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Account.java

@@ -125,6 +125,21 @@ public final class Account {
       Integer id = RefNames.parseShardedRefPart(name);
       return id != null ? new Account.Id(id) : null;
     }
+
+    /**
+     * Parse an Account.Id out of the last part of a ref name.
+     * <p>
+     * The input is a ref name of the form {@code ".../1234"}, where the suffix
+     * is a non-sharded account ID. Ref names using a sharded ID should use
+     * {@link #fromRefPart(String)} instead for greater safety.
+     *
+     * @param name ref name
+     * @return account ID, or null if not numeric.
+     */
+    public static Id fromRefSuffix(String name) {
+      Integer id = RefNames.parseRefSuffix(name);
+      return id != null ? new Account.Id(id) : null;
+    }
   }
 
   @Column(id = 1)

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/Change.java

@@ -163,6 +163,11 @@ public final class Change {
       return new Change.Id(Integer.parseInt(id));
     }
 
+    public static Id fromRefPart(String ref) {
+      Integer id = RefNames.parseShardedRefPart(ref);
+      return id != null ? new Change.Id(id) : null;
+    }
+
     static int startIndex(String ref) {
       if (ref == null || !ref.startsWith(REFS_CHANGES)) {
         return -1;

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/RefNames.java

@@ -107,15 +107,15 @@ public class RefNames {
     return r.toString();
   }
 
-  public static String refsDraftComments(Account.Id accountId,
+  public static String refsDraftComments(Change.Id changeId,
-      Change.Id changeId) {
+      Account.Id accountId) {
-    StringBuilder r = buildRefsPrefix(REFS_DRAFT_COMMENTS, accountId.get());
+    StringBuilder r = buildRefsPrefix(REFS_DRAFT_COMMENTS, changeId.get());
-    r.append(changeId.get());
+    r.append(accountId.get());
     return r.toString();
   }
 
-  public static String refsDraftCommentsPrefix(Account.Id accountId) {
+  public static String refsDraftCommentsPrefix(Change.Id changeId) {
-    return buildRefsPrefix(REFS_DRAFT_COMMENTS, accountId.get()).toString();
+    return buildRefsPrefix(REFS_DRAFT_COMMENTS, changeId.get()).toString();
   }
 
   public static String refsStarredChanges(Change.Id changeId,
@@ -217,6 +217,26 @@ public class RefNames {
     return id;
   }
 
+  static Integer parseRefSuffix(String name) {
+    if (name == null) {
+      return null;
+    }
+    int i = name.length();
+    while (i > 0) {
+      char c = name.charAt(i - 1);
+      if (c == '/') {
+        break;
+      } else if (!Character.isDigit(c)) {
+        return null;
+      }
+      i--;
+    }
+    if (i == 0) {
+      return null;
+    }
+    return Integer.valueOf(name.substring(i, name.length()));
+  }
+
   private RefNames() {
   }
 }

gerrit-reviewdb/src/test/java/com/google/gerrit/reviewdb/client/AccountTest.java

@@ -17,6 +17,7 @@ package com.google.gerrit.reviewdb.client;
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.gerrit.reviewdb.client.Account.Id.fromRef;
 import static com.google.gerrit.reviewdb.client.Account.Id.fromRefPart;
+import static com.google.gerrit.reviewdb.client.Account.Id.fromRefSuffix;
 
 import org.junit.Test;
 
@@ -48,6 +49,12 @@ public class AccountTest {
     assertThat(fromRefPart("ab/cd")).isNull();
   }
 
+  @Test
+  public void parseRefSuffix() {
+    assertThat(fromRefSuffix("12/34")).isEqualTo(id(34));
+    assertThat(fromRefSuffix("ab/cd")).isNull();
+  }
+
   private Account.Id id(int n) {
     return new Account.Id(n);
   }

gerrit-reviewdb/src/test/java/com/google/gerrit/reviewdb/client/RefNamesTest.java

@@ -16,6 +16,7 @@ package com.google.gerrit.reviewdb.client;
 
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.gerrit.reviewdb.client.RefNames.parseShardedRefPart;
+import static com.google.gerrit.reviewdb.client.RefNames.parseRefSuffix;
 
 import org.junit.Test;
 
@@ -39,14 +40,14 @@ public class RefNamesTest {
 
   @Test
   public void refsDraftComments() throws Exception {
-    assertThat(RefNames.refsDraftComments(accountId, changeId))
+    assertThat(RefNames.refsDraftComments(changeId, accountId))
-      .isEqualTo("refs/draft-comments/23/1011123/67473");
+      .isEqualTo("refs/draft-comments/73/67473/1011123");
   }
 
   @Test
   public void refsDraftCommentsPrefix() throws Exception {
-    assertThat(RefNames.refsDraftCommentsPrefix(accountId))
+    assertThat(RefNames.refsDraftCommentsPrefix(changeId))
-      .isEqualTo("refs/draft-comments/23/1011123/");
+      .isEqualTo("refs/draft-comments/73/67473/");
   }
 
   @Test
@@ -89,4 +90,19 @@ public class RefNamesTest {
     // Shard too short.
     assertThat(parseShardedRefPart("1/1")).isNull();
   }
+
+  @Test
+  public void testParseRefSuffix() throws Exception {
+    assertThat(parseRefSuffix("1/2/34")).isEqualTo(34);
+    assertThat(parseRefSuffix("/34")).isEqualTo(34);
+
+    assertThat(parseRefSuffix(null)).isNull();
+    assertThat(parseRefSuffix("")).isNull();
+    assertThat(parseRefSuffix("34")).isNull();
+    assertThat(parseRefSuffix("12/ab")).isNull();
+    assertThat(parseRefSuffix("12/a4")).isNull();
+    assertThat(parseRefSuffix("12/4a")).isNull();
+    assertThat(parseRefSuffix("a4")).isNull();
+    assertThat(parseRefSuffix("4a")).isNull();
+  }
 }

gerrit-server/src/main/java/com/google/gerrit/server/PatchLineCommentsUtil.java

@@ -23,7 +23,6 @@ import com.google.common.collect.ComparisonChain;
 import com.google.common.collect.FluentIterable;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
-import com.google.common.collect.Maps;
 import com.google.common.collect.Ordering;
 import com.google.gerrit.extensions.client.Side;
 import com.google.gerrit.extensions.common.CommentInfo;
@@ -52,7 +51,6 @@ import org.eclipse.jgit.lib.BatchRefUpdate;
 import org.eclipse.jgit.lib.NullProgressMonitor;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
-import org.eclipse.jgit.lib.RefDatabase;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevWalk;
 import org.eclipse.jgit.transport.ReceiveCommand;
@@ -62,8 +60,6 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
-import java.util.Map;
-import java.util.Set;
 
 /**
  * Utility functions to manipulate PatchLineComments.
@@ -169,8 +165,8 @@ public class PatchLineCommentsUtil {
     }
 
     List<PatchLineComment> comments = Lists.newArrayList();
-    for (String refSuffix : getDraftRefs(notes.getChangeId()).keySet()) {
+    for (Ref ref : getDraftRefs(notes.getChangeId())) {
-      Account.Id account = Account.Id.fromRefPart(refSuffix);
+      Account.Id account = Account.Id.fromRefSuffix(ref.getName());
       if (account != null) {
         comments.addAll(draftByChangeAuthor(db, notes, account));
       }
@@ -199,8 +195,8 @@ public class PatchLineCommentsUtil {
     List<PatchLineComment> comments = Lists.newArrayList();
     comments.addAll(publishedByPatchSet(db, notes, psId));
 
-    for (String refSuffix : getDraftRefs(notes.getChangeId()).keySet()) {
+    for (Ref ref : getDraftRefs(notes.getChangeId())) {
-      Account.Id account = Account.Id.fromRefPart(refSuffix);
+      Account.Id account = Account.Id.fromRefSuffix(ref.getName());
       if (account != null) {
         comments.addAll(draftByPatchSetAuthor(db, psId, account, notes));
       }
@@ -278,18 +274,25 @@ public class PatchLineCommentsUtil {
       return sort(db.patchComments().draftByAuthor(author).toList());
     }
 
-    Set<String> refNames =
-        getRefNamesAllUsers(RefNames.refsDraftCommentsPrefix(author));
     List<PatchLineComment> comments = Lists.newArrayList();
-    for (String refName : refNames) {
+    try (Repository repo = repoManager.openRepository(allUsers)) {
-      Change.Id changeId = Change.Id.parse(refName);
+      for (String refName : repo.getRefDatabase()
+          .getRefs(RefNames.REFS_DRAFT_COMMENTS).keySet()) {
+        Account.Id accountId = Account.Id.fromRefSuffix(refName);
+        Change.Id changeId = Change.Id.fromRefPart(refName);
+        if (accountId == null || changeId == null) {
+          continue;
+        }
         // Avoid loading notes for all affected changes just to be able to auto-
-      // rebuild. This is only used in a corner case in the search codepath, so
+        // rebuild. This is only used in a corner case in the search codepath,
-      // returning slightly stale values is ok.
+        // so returning slightly stale values is ok.
         DraftCommentNotes notes =
             draftFactory.createWithAutoRebuildingDisabled(changeId, author);
         comments.addAll(notes.load().getComments().values());
       }
+    } catch (IOException e) {
+      throw new OrmException(e);
+    }
     return sort(comments);
   }
 
@@ -314,7 +317,7 @@ public class PatchLineCommentsUtil {
     try (Repository repo = repoManager.openRepository(allUsers);
         RevWalk rw = new RevWalk(repo)) {
       BatchRefUpdate bru = repo.getRefDatabase().newBatchUpdate();
-      for (Ref ref : getDraftRefs(repo, changeId).values()) {
+      for (Ref ref : getDraftRefs(repo, changeId)) {
         bru.addCommand(new ReceiveCommand(
             ref.getObjectId(), ObjectId.zeroId(), ref.getName()));
       }
@@ -372,16 +375,7 @@ public class PatchLineCommentsUtil {
     return c.getRevId();
   }
 
-  private Set<String> getRefNamesAllUsers(String prefix) throws OrmException {
+  public Collection<Ref> getDraftRefs(Change.Id changeId)
-    try (Repository repo = repoManager.openRepository(allUsers)) {
-      RefDatabase refDb = repo.getRefDatabase();
-      return refDb.getRefs(prefix).keySet();
-    } catch (IOException e) {
-      throw new OrmException(e);
-    }
-  }
-
-  public Map<String, Ref> getDraftRefs(Change.Id changeId)
       throws OrmException {
     try (Repository repo = repoManager.openRepository(allUsers)) {
       return getDraftRefs(repo, changeId);
@@ -390,17 +384,10 @@ public class PatchLineCommentsUtil {
     }
   }
 
-  private Map<String, Ref> getDraftRefs(Repository repo,
+  private Collection<Ref> getDraftRefs(Repository repo, Change.Id changeId)
-      final Change.Id changeId) throws IOException {
+      throws IOException {
-    final String suffix = "/" + changeId.get();
+    return repo.getRefDatabase().getRefs(
-    return Maps.filterKeys(
+        RefNames.refsDraftCommentsPrefix(changeId)).values();
-        repo.getRefDatabase().getRefs(RefNames.REFS_DRAFT_COMMENTS),
-        new Predicate<String>() {
-          @Override
-          public boolean apply(String input) {
-            return input.endsWith(suffix);
-          }
-        });
   }
 
   private static List<PatchLineComment> sort(List<PatchLineComment> comments) {

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

@@ -221,7 +221,7 @@ public class ChangeDraftUpdate extends AbstractChangeUpdate {
 
   @Override
   protected String getRefName() {
-    return RefNames.refsDraftComments(accountId, getId());
+    return RefNames.refsDraftComments(getId(), accountId);
   }
 
   @Override

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

@@ -110,7 +110,7 @@ public class DraftCommentNotes extends AbstractChangeNotes<DraftCommentNotes> {
 
   @Override
   protected String getRefName() {
-    return RefNames.refsDraftComments(author, getChangeId());
+    return RefNames.refsDraftComments(getChangeId(), author);
   }
 
   @Override

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

@@ -177,7 +177,7 @@ public class NoteDbChangeState {
   public boolean areDraftsUpToDate(Repository draftsRepo, Account.Id accountId)
       throws IOException {
     Ref ref = draftsRepo.exactRef(
-        RefNames.refsDraftComments(accountId, changeId));
+        RefNames.refsDraftComments(changeId, accountId));
     if (ref == null) {
       return !draftIds.containsKey(accountId);
     }

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

@@ -258,12 +258,10 @@ public class NoteDbUpdateManager {
     for (ReceiveCommand cmd : allUsersRepo.cmds.getCommands().values()) {
       String r = cmd.getRefName();
       if (r.startsWith(REFS_DRAFT_COMMENTS)) {
-        Account.Id accountId =
+        Change.Id changeId =
-            Account.Id.fromRefPart(r.substring(REFS_DRAFT_COMMENTS.length()));
+            Change.Id.fromRefPart(r.substring(REFS_DRAFT_COMMENTS.length()));
-        checkDraftRef(accountId != null, r);
+        Account.Id accountId = Account.Id.fromRefSuffix(r);
-        int s = r.lastIndexOf('/');
+        checkDraftRef(accountId != null && changeId != null, r);
-        checkDraftRef(s >= 0 && s < r.length() - 1, r);
-        Change.Id changeId = Change.Id.parse(r.substring(s + 1));
         draftIds.put(changeId, accountId, cmd.getNewId());
       }
     }

gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeNotesTest.java

@@ -1878,7 +1878,7 @@ public class ChangeNotesTest extends AbstractChangeNotesTest {
     update.commit();
 
     assertThat(repo.exactRef(changeMetaRef(c.getId()))).isNotNull();
-    String draftRef = refsDraftComments(otherUser.getAccountId(), c.getId());
+    String draftRef = refsDraftComments(c.getId(), otherUser.getAccountId());
     assertThat(exactRefAllUsers(draftRef)).isNull();
   }
 
@@ -1900,7 +1900,7 @@ public class ChangeNotesTest extends AbstractChangeNotesTest {
     update.putComment(draft);
     update.commit();
 
-    String draftRef = refsDraftComments(otherUser.getAccountId(), c.getId());
+    String draftRef = refsDraftComments(c.getId(), otherUser.getAccountId());
     ObjectId old = exactRefAllUsers(draftRef);
     assertThat(old).isNotNull();
 
@@ -2074,7 +2074,7 @@ public class ChangeNotesTest extends AbstractChangeNotesTest {
     update.putComment(comment2);
     update.commit();
 
-    String refName = refsDraftComments(otherUserId, c.getId());
+    String refName = refsDraftComments(c.getId(), otherUserId);
     ObjectId oldDraftId = exactRefAllUsers(refName);
 
     update = newUpdate(c, otherUser);