Merge "Avoid lucene index deletes during offline reindexing" into stable-3.2

19 files changed, 183 insertions, 13 deletions

diff --git a/java/com/google/gerrit/acceptance/DisabledAccountIndex.java b/java/com/google/gerrit/acceptance/DisabledAccountIndex.java
index 271d15c176..7bd0c73013 100644
--- a/java/com/google/gerrit/acceptance/DisabledAccountIndex.java
+++ b/java/com/google/gerrit/acceptance/DisabledAccountIndex.java
@@ -45,6 +45,11 @@ public class DisabledAccountIndex implements AccountIndex {
   }
 
   @Override
+  public void insert(AccountState obj) {
+    throw new UnsupportedOperationException("AccountIndex is disabled");
+  }
+
+  @Override
   public void replace(AccountState obj) {
     throw new UnsupportedOperationException("AccountIndex is disabled");
   }
diff --git a/java/com/google/gerrit/acceptance/DisabledChangeIndex.java b/java/com/google/gerrit/acceptance/DisabledChangeIndex.java
index 34f72f5ccf..7671ad4068 100644
--- a/java/com/google/gerrit/acceptance/DisabledChangeIndex.java
+++ b/java/com/google/gerrit/acceptance/DisabledChangeIndex.java
@@ -52,6 +52,11 @@ public class DisabledChangeIndex implements ChangeIndex {
   }
 
   @Override
+  public void insert(ChangeData obj) {
+    throw new UnsupportedOperationException("ChangeIndex is disabled");
+  }
+
+  @Override
   public void replace(ChangeData obj) {
     throw new UnsupportedOperationException("ChangeIndex is disabled");
   }
diff --git a/java/com/google/gerrit/acceptance/DisabledProjectIndex.java b/java/com/google/gerrit/acceptance/DisabledProjectIndex.java
index ed119ff3bc..2e3dd906b6 100644
--- a/java/com/google/gerrit/acceptance/DisabledProjectIndex.java
+++ b/java/com/google/gerrit/acceptance/DisabledProjectIndex.java
@@ -50,6 +50,11 @@ public class DisabledProjectIndex implements ProjectIndex {
   }
 
   @Override
+  public void insert(ProjectData obj) {
+    throw new UnsupportedOperationException("ProjectIndex is disabled");
+  }
+
+  @Override
   public void replace(ProjectData obj) {
     throw new UnsupportedOperationException("ProjectIndex is disabled");
   }
diff --git a/java/com/google/gerrit/acceptance/ReadOnlyChangeIndex.java b/java/com/google/gerrit/acceptance/ReadOnlyChangeIndex.java
index e943519d19..f7a0669739 100644
--- a/java/com/google/gerrit/acceptance/ReadOnlyChangeIndex.java
+++ b/java/com/google/gerrit/acceptance/ReadOnlyChangeIndex.java
@@ -45,6 +45,11 @@ class ReadOnlyChangeIndex implements ChangeIndex {
   }
 
   @Override
+  public void insert(ChangeData obj) {
+    // do nothing
+  }
+
+  @Override
   public void replace(ChangeData obj) {
     // do nothing
   }
diff --git a/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java b/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java
index e56f470300..d53490b8f6 100644
--- a/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java
+++ b/java/com/google/gerrit/elasticsearch/AbstractElasticIndex.java
@@ -175,6 +175,12 @@ abstract class AbstractElasticIndex<K, V> implements Index<K, V> {
   }
 
   @Override
+  public void insert(V obj) {
+    // TODO: Implement real insert() if it helps performance
+    replace(obj);
+  }
+
+  @Override
   public void deleteAll() {
     // Delete the index, if it exists.
     String endpoint = indexName + client.adapter().indicesExistParams();
diff --git a/java/com/google/gerrit/index/Index.java b/java/com/google/gerrit/index/Index.java
index 44f8b4236e..e662bc8477 100644
--- a/java/com/google/gerrit/index/Index.java
+++ b/java/com/google/gerrit/index/Index.java
@@ -40,6 +40,16 @@ public interface Index<K, V> {
   void close();
 
   /**
+   * Insert a document into the index.
+   *
+   * <p>Results may not be immediately visible to searchers, but should be visible within a
+   * reasonable amount of time.
+   *
+   * @param obj document object
+   */
+  void insert(V obj);
+
+  /**
    * Update a document in the index.
    *
    * <p>Semantically equivalent to deleting the document and reinserting it with new field values. A
diff --git a/java/com/google/gerrit/lucene/ChangeSubIndex.java b/java/com/google/gerrit/lucene/ChangeSubIndex.java
index 5c24b9a009..360331a7bd 100644
--- a/java/com/google/gerrit/lucene/ChangeSubIndex.java
+++ b/java/com/google/gerrit/lucene/ChangeSubIndex.java
@@ -89,6 +89,11 @@ public class ChangeSubIndex extends AbstractLuceneIndex<Change.Id, ChangeData>
   }
 
   @Override
+  public void insert(ChangeData obj) {
+    throw new UnsupportedOperationException("don't use ChangeSubIndex directly");
+  }
+
+  @Override
   public void replace(ChangeData obj) {
     throw new UnsupportedOperationException("don't use ChangeSubIndex directly");
   }
diff --git a/java/com/google/gerrit/lucene/LuceneAccountIndex.java b/java/com/google/gerrit/lucene/LuceneAccountIndex.java
index 87b7ccef6b..c4a524060d 100644
--- a/java/com/google/gerrit/lucene/LuceneAccountIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneAccountIndex.java
@@ -144,6 +144,15 @@ public class LuceneAccountIndex extends AbstractLuceneIndex<Account.Id, AccountS
   }
 
   @Override
+  public void insert(AccountState as) {
+    try {
+      insert(toDocument(as)).get();
+    } catch (ExecutionException | InterruptedException e) {
+      throw new StorageException(e);
+    }
+  }
+
+  @Override
   public void delete(Account.Id key) {
     try {
       delete(idTerm(getSchema().useLegacyNumericFields(), key)).get();
diff --git a/java/com/google/gerrit/lucene/LuceneChangeIndex.java b/java/com/google/gerrit/lucene/LuceneChangeIndex.java
index bb97936bad..78f4624a91 100644
--- a/java/com/google/gerrit/lucene/LuceneChangeIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneChangeIndex.java
@@ -287,6 +287,23 @@ public class LuceneChangeIndex implements ChangeIndex {
   }
 
   @Override
+  public void insert(ChangeData cd) {
+    Term id = LuceneChangeIndex.idTerm(idTerm, idField, cd);
+    // toDocument is essentially static and doesn't depend on the specific
+    // sub-index, so just pick one.
+    Document doc = openIndex.toDocument(cd);
+    try {
+      if (cd.change().isNew()) {
+        openIndex.insert(doc).get();
+      } else {
+        closedIndex.insert(doc).get();
+      }
+    } catch (ExecutionException | InterruptedException e) {
+      throw new StorageException(e);
+    }
+  }
+
+  @Override
   public void delete(Change.Id changeId) {
     Term id = LuceneChangeIndex.idTerm(idTerm, idField, changeId);
     try {
diff --git a/java/com/google/gerrit/lucene/LuceneGroupIndex.java b/java/com/google/gerrit/lucene/LuceneGroupIndex.java
index c1b44c7829..9f8b62e741 100644
--- a/java/com/google/gerrit/lucene/LuceneGroupIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneGroupIndex.java
@@ -125,6 +125,15 @@ public class LuceneGroupIndex extends AbstractLuceneIndex<AccountGroup.UUID, Int
   }
 
   @Override
+  public void insert(InternalGroup group) {
+    try {
+      insert(toDocument(group)).get();
+    } catch (ExecutionException | InterruptedException e) {
+      throw new StorageException(e);
+    }
+  }
+
+  @Override
   public void delete(AccountGroup.UUID key) {
     try {
       delete(idTerm(key)).get();
diff --git a/java/com/google/gerrit/lucene/LuceneProjectIndex.java b/java/com/google/gerrit/lucene/LuceneProjectIndex.java
index 7e7aecb923..11707be379 100644
--- a/java/com/google/gerrit/lucene/LuceneProjectIndex.java
+++ b/java/com/google/gerrit/lucene/LuceneProjectIndex.java
@@ -125,6 +125,15 @@ public class LuceneProjectIndex extends AbstractLuceneIndex<Project.NameKey, Pro
   }
 
   @Override
+  public void insert(ProjectData projectState) {
+    try {
+      insert(toDocument(projectState)).get();
+    } catch (ExecutionException | InterruptedException e) {
+      throw new StorageException(e);
+    }
+  }
+
+  @Override
   public void delete(Project.NameKey nameKey) {
     try {
       delete(idTerm(nameKey)).get();
diff --git a/java/com/google/gerrit/pgm/Reindex.java b/java/com/google/gerrit/pgm/Reindex.java
index 8eaf3b3094..e8be0e6af5 100644
--- a/java/com/google/gerrit/pgm/Reindex.java
+++ b/java/com/google/gerrit/pgm/Reindex.java
@@ -38,12 +38,15 @@ import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.index.IndexModule;
 import com.google.gerrit.server.index.change.ChangeSchemaDefinitions;
 import com.google.gerrit.server.index.options.AutoFlush;
+import com.google.gerrit.server.index.options.IsFirstInsertForEntry;
 import com.google.gerrit.server.plugins.PluginGuiceEnvironment;
 import com.google.gerrit.server.util.ReplicaUtil;
+import com.google.inject.AbstractModule;
 import com.google.inject.Inject;
 import com.google.inject.Injector;
 import com.google.inject.Key;
 import com.google.inject.Module;
+import com.google.inject.multibindings.OptionalBinder;
 import java.io.StringWriter;
 import java.io.Writer;
 import java.util.ArrayList;
@@ -172,6 +175,16 @@ public class Reindex extends SiteProgram {
       throw new IllegalStateException("unsupported index.type = " + indexType);
     }
     modules.add(indexModule);
+    modules.add(
+        new AbstractModule() {
+          @Override
+          protected void configure() {
+            super.configure();
+            OptionalBinder.newOptionalBinder(binder(), IsFirstInsertForEntry.class)
+                .setBinding()
+                .toInstance(IsFirstInsertForEntry.YES);
+          }
+        });
     modules.add(new BatchProgramModule());
     modules.add(
         new FactoryModule() {
diff --git a/java/com/google/gerrit/server/index/IndexModule.java b/java/com/google/gerrit/server/index/IndexModule.java
index 17665c0903..8b04c8dede 100644
--- a/java/com/google/gerrit/server/index/IndexModule.java
+++ b/java/com/google/gerrit/server/index/IndexModule.java
@@ -51,6 +51,7 @@ import com.google.gerrit.server.index.group.GroupIndexRewriter;
 import com.google.gerrit.server.index.group.GroupIndexer;
 import com.google.gerrit.server.index.group.GroupIndexerImpl;
 import com.google.gerrit.server.index.group.GroupSchemaDefinitions;
+import com.google.gerrit.server.index.options.IsFirstInsertForEntry;
 import com.google.gerrit.server.index.project.ProjectIndexDefinition;
 import com.google.gerrit.server.index.project.ProjectIndexerImpl;
 import com.google.inject.Inject;
@@ -59,6 +60,7 @@ import com.google.inject.Key;
 import com.google.inject.Provides;
 import com.google.inject.ProvisionException;
 import com.google.inject.Singleton;
+import com.google.inject.multibindings.OptionalBinder;
 import java.util.Collection;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
@@ -143,6 +145,9 @@ public class IndexModule extends LifecycleModule {
     }
 
     DynamicSet.setOf(binder(), OnlineUpgradeListener.class);
+    OptionalBinder.newOptionalBinder(binder(), IsFirstInsertForEntry.class)
+        .setDefault()
+        .toInstance(IsFirstInsertForEntry.NO);
   }
 
   @Provides
diff --git a/java/com/google/gerrit/server/index/account/AllAccountsIndexer.java b/java/com/google/gerrit/server/index/account/AllAccountsIndexer.java
index 63889b798d..ec27db0f1f 100644
--- a/java/com/google/gerrit/server/index/account/AllAccountsIndexer.java
+++ b/java/com/google/gerrit/server/index/account/AllAccountsIndexer.java
@@ -27,6 +27,7 @@ import com.google.gerrit.server.account.AccountCache;
 import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.account.Accounts;
 import com.google.gerrit.server.index.IndexExecutor;
+import com.google.gerrit.server.index.options.IsFirstInsertForEntry;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import java.io.IOException;
@@ -50,15 +51,18 @@ public class AllAccountsIndexer extends SiteIndexer<Account.Id, AccountState, Ac
   private final ListeningExecutorService executor;
   private final Accounts accounts;
   private final AccountCache accountCache;
+  private final IsFirstInsertForEntry isFirstInsertForEntry;
 
   @Inject
   AllAccountsIndexer(
       @IndexExecutor(BATCH) ListeningExecutorService executor,
       Accounts accounts,
-      AccountCache accountCache) {
+      AccountCache accountCache,
+      IsFirstInsertForEntry isFirstInsertForEntry) {
     this.executor = executor;
     this.accounts = accounts;
     this.accountCache = accountCache;
+    this.isFirstInsertForEntry = isFirstInsertForEntry;
   }
 
   @Override
@@ -92,7 +96,11 @@ public class AllAccountsIndexer extends SiteIndexer<Account.Id, AccountState, Ac
                 try {
                   Optional<AccountState> a = accountCache.get(id);
                   if (a.isPresent()) {
-                    index.replace(a.get());
+                    if (isFirstInsertForEntry.equals(isFirstInsertForEntry.YES)) {
+                      index.insert(a.get());
+                    } else {
+                      index.replace(a.get());
+                    }
                   } else {
                     index.delete(id);
                   }
diff --git a/java/com/google/gerrit/server/index/change/ChangeIndexer.java b/java/com/google/gerrit/server/index/change/ChangeIndexer.java
index e0f6bec8e1..a088af02e0 100644
--- a/java/com/google/gerrit/server/index/change/ChangeIndexer.java
+++ b/java/com/google/gerrit/server/index/change/ChangeIndexer.java
@@ -30,6 +30,7 @@ import com.google.gerrit.index.Index;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.index.IndexExecutor;
 import com.google.gerrit.server.index.StalenessCheckResult;
+import com.google.gerrit.server.index.options.IsFirstInsertForEntry;
 import com.google.gerrit.server.logging.Metadata;
 import com.google.gerrit.server.logging.TraceContext;
 import com.google.gerrit.server.logging.TraceContext.TraceTimer;
@@ -78,6 +79,7 @@ public class ChangeIndexer {
   private final PluginSetContext<ChangeIndexedListener> indexedListeners;
   private final StalenessChecker stalenessChecker;
   private final boolean autoReindexIfStale;
+  private final IsFirstInsertForEntry isFirstInsertForEntry;
 
   private final Set<IndexTask> queuedIndexTasks =
       Collections.newSetFromMap(new ConcurrentHashMap<>());
@@ -94,7 +96,8 @@ public class ChangeIndexer {
       StalenessChecker stalenessChecker,
       @IndexExecutor(BATCH) ListeningExecutorService batchExecutor,
       @Assisted ListeningExecutorService executor,
-      @Assisted ChangeIndex index) {
+      @Assisted ChangeIndex index,
+      IsFirstInsertForEntry isFirstInsertForEntry) {
     this.executor = executor;
     this.changeDataFactory = changeDataFactory;
     this.notesFactory = notesFactory;
@@ -105,6 +108,7 @@ public class ChangeIndexer {
     this.autoReindexIfStale = autoReindexIfStale(cfg);
     this.index = index;
     this.indexes = null;
+    this.isFirstInsertForEntry = isFirstInsertForEntry;
   }
 
   @AssistedInject
@@ -117,7 +121,8 @@ public class ChangeIndexer {
       StalenessChecker stalenessChecker,
       @IndexExecutor(BATCH) ListeningExecutorService batchExecutor,
       @Assisted ListeningExecutorService executor,
-      @Assisted ChangeIndexCollection indexes) {
+      @Assisted ChangeIndexCollection indexes,
+      IsFirstInsertForEntry isFirstInsertForEntry) {
     this.executor = executor;
     this.changeDataFactory = changeDataFactory;
     this.notesFactory = notesFactory;
@@ -128,6 +133,7 @@ public class ChangeIndexer {
     this.autoReindexIfStale = autoReindexIfStale(cfg);
     this.index = null;
     this.indexes = indexes;
+    this.isFirstInsertForEntry = isFirstInsertForEntry;
   }
 
   private static boolean autoReindexIfStale(Config cfg) {
@@ -198,21 +204,25 @@ public class ChangeIndexer {
   }
 
   private void indexImpl(ChangeData cd) {
-    logger.atFine().log("Replace change %d in index.", cd.getId().get());
+    logger.atFine().log("Reindex change %d in index.", cd.getId().get());
     for (Index<?, ChangeData> i : getWriteIndexes()) {
       try (TraceTimer traceTimer =
           TraceContext.newTimer(
-              "Replacing change in index",
+              "Reindexing change in index",
               Metadata.builder()
                   .changeId(cd.getId().get())
                   .patchSetId(cd.currentPatchSet().number())
                   .indexVersion(i.getSchema().getVersion())
                   .build())) {
-        i.replace(cd);
+        if (isFirstInsertForEntry.equals(isFirstInsertForEntry.YES)) {
+          i.insert(cd);
+        } else {
+          i.replace(cd);
+        }
       } catch (RuntimeException e) {
         throw new StorageException(
             String.format(
-                "Failed to replace change %d in index version %d (current patch set = %d)",
+                "Failed to reindex change %d in index version %d (current patch set = %d)",
                 cd.getId().get(), i.getSchema().getVersion(), cd.currentPatchSet().number()),
             e);
       }
diff --git a/java/com/google/gerrit/server/index/group/AllGroupsIndexer.java b/java/com/google/gerrit/server/index/group/AllGroupsIndexer.java
index 51c7730640..84d6a9d77c 100644
--- a/java/com/google/gerrit/server/index/group/AllGroupsIndexer.java
+++ b/java/com/google/gerrit/server/index/group/AllGroupsIndexer.java
@@ -30,6 +30,7 @@ import com.google.gerrit.server.group.InternalGroup;
 import com.google.gerrit.server.group.db.Groups;
 import com.google.gerrit.server.group.db.GroupsNoteDbConsistencyChecker;
 import com.google.gerrit.server.index.IndexExecutor;
+import com.google.gerrit.server.index.options.IsFirstInsertForEntry;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import java.io.IOException;
@@ -54,15 +55,18 @@ public class AllGroupsIndexer extends SiteIndexer<AccountGroup.UUID, InternalGro
   private final ListeningExecutorService executor;
   private final GroupCache groupCache;
   private final Groups groups;
+  private final IsFirstInsertForEntry isFirstInsertForEntry;
 
   @Inject
   AllGroupsIndexer(
       @IndexExecutor(BATCH) ListeningExecutorService executor,
       GroupCache groupCache,
-      Groups groups) {
+      Groups groups,
+      IsFirstInsertForEntry isFirstInsertForEntry) {
     this.executor = executor;
     this.groupCache = groupCache;
     this.groups = groups;
+    this.isFirstInsertForEntry = isFirstInsertForEntry;
   }
 
   @Override
@@ -97,7 +101,11 @@ public class AllGroupsIndexer extends SiteIndexer<AccountGroup.UUID, InternalGro
                   groupCache.evict(uuid);
                   Optional<InternalGroup> internalGroup = groupCache.get(uuid);
                   if (internalGroup.isPresent()) {
-                    index.replace(internalGroup.get());
+                    if (isFirstInsertForEntry.equals(isFirstInsertForEntry.YES)) {
+                      index.insert(internalGroup.get());
+                    } else {
+                      index.replace(internalGroup.get());
+                    }
                   } else {
                     index.delete(uuid);
 
diff --git a/java/com/google/gerrit/server/index/options/IsFirstInsertForEntry.java b/java/com/google/gerrit/server/index/options/IsFirstInsertForEntry.java
new file mode 100644
index 0000000000..f943309e07
--- /dev/null
+++ b/java/com/google/gerrit/server/index/options/IsFirstInsertForEntry.java
@@ -0,0 +1,26 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.index.options;
+
+/**
+ * This enum should be injected and checked to decide on which operation ({@link
+ * com.google.gerrit.index.Index#replace(Object) replace()} or {@link
+ * com.google.gerrit.index.Index#insert(Object) insert()}) should be performed on a specific {@link
+ * com.google.gerrit.index.Index index}.
+ */
+public enum IsFirstInsertForEntry {
+  YES,
+  NO
+}
diff --git a/java/com/google/gerrit/server/index/project/AllProjectsIndexer.java b/java/com/google/gerrit/server/index/project/AllProjectsIndexer.java
index 0e4b688d6c..86c7e94230 100644
--- a/java/com/google/gerrit/server/index/project/AllProjectsIndexer.java
+++ b/java/com/google/gerrit/server/index/project/AllProjectsIndexer.java
@@ -27,6 +27,7 @@ import com.google.gerrit.index.SiteIndexer;
 import com.google.gerrit.index.project.ProjectData;
 import com.google.gerrit.index.project.ProjectIndex;
 import com.google.gerrit.server.index.IndexExecutor;
+import com.google.gerrit.server.index.options.IsFirstInsertForEntry;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
@@ -48,12 +49,16 @@ public class AllProjectsIndexer extends SiteIndexer<Project.NameKey, ProjectData
 
   private final ListeningExecutorService executor;
   private final ProjectCache projectCache;
+  private final IsFirstInsertForEntry isFirstInsertForEntry;
 
   @Inject
   AllProjectsIndexer(
-      @IndexExecutor(BATCH) ListeningExecutorService executor, ProjectCache projectCache) {
+      @IndexExecutor(BATCH) ListeningExecutorService executor,
+      ProjectCache projectCache,
+      IsFirstInsertForEntry isFirstInsertForEntry) {
     this.executor = executor;
     this.projectCache = projectCache;
+    this.isFirstInsertForEntry = isFirstInsertForEntry;
   }
 
   @Override
@@ -79,8 +84,13 @@ public class AllProjectsIndexer extends SiteIndexer<Project.NameKey, ProjectData
               () -> {
                 try {
                   projectCache.evict(name);
-                  index.replace(
-                      projectCache.get(name).orElseThrow(illegalState(name)).toProjectData());
+                  ProjectData projectData =
+                      projectCache.get(name).orElseThrow(illegalState(name)).toProjectData();
+                  if (isFirstInsertForEntry.equals(isFirstInsertForEntry.YES)) {
+                    index.insert(projectData);
+                  } else {
+                    index.replace(projectData);
+                  }
                   verboseWriter.println("Reindexed " + desc);
                   done.incrementAndGet();
                 } catch (Exception e) {
diff --git a/javatests/com/google/gerrit/server/index/change/FakeChangeIndex.java b/javatests/com/google/gerrit/server/index/change/FakeChangeIndex.java
index a23ccaba9a..fc56a3c00f 100644
--- a/javatests/com/google/gerrit/server/index/change/FakeChangeIndex.java
+++ b/javatests/com/google/gerrit/server/index/change/FakeChangeIndex.java
@@ -74,6 +74,11 @@ public class FakeChangeIndex implements ChangeIndex {
   }
 
   @Override
+  public void insert(ChangeData obj) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
   public void replace(ChangeData cd) {
     throw new UnsupportedOperationException();
   }