Reindex: add --dry-run flag

We are working on evaluating performance of Lucene indexing, and want
to be able to separate the cost of Gerrit-specific operations from the
cost of Lucene operations. This flag prevents any writing to the
Lucene indexes, which will help with that. We may want to remove this
flag eventually.

Change-Id: I0e68f26c5d89c1c9b1b0b5d082af3b9241ce8d80

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneChangeIndex.java

@@ -43,8 +43,6 @@ import com.google.gerrit.server.query.change.ChangeDataSource;
 import com.google.gerrit.server.query.change.IndexRewriteImpl;
 import com.google.gwtorm.server.OrmException;
 import com.google.gwtorm.server.ResultSet;
-import com.google.inject.Inject;
-import com.google.inject.Singleton;
 
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
@@ -76,19 +74,20 @@ import java.util.Set;
  * though there may be some lag between a committed write and it showing up to
  * other threads' searchers.
  */
-@Singleton
 public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
   public static final Version LUCENE_VERSION = Version.LUCENE_43;
   public static final String CHANGES_OPEN = "changes_open";
   public static final String CHANGES_CLOSED = "changes_closed";
 
   private final FillArgs fillArgs;
+  private final boolean readOnly;
   private final SubIndex openIndex;
   private final SubIndex closedIndex;
 
-  @Inject
-  LuceneChangeIndex(SitePaths sitePaths, FillArgs fillArgs) throws IOException {
+  LuceneChangeIndex(SitePaths sitePaths, FillArgs fillArgs, boolean readOnly)
+      throws IOException {
     this.fillArgs = fillArgs;
+    this.readOnly = readOnly;
     openIndex = new SubIndex(new File(sitePaths.index_dir, CHANGES_OPEN));
     closedIndex = new SubIndex(new File(sitePaths.index_dir, CHANGES_CLOSED));
   }
@@ -108,6 +107,9 @@ public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
   public void insert(ChangeData cd) throws IOException {
     Term id = idTerm(cd);
     Document doc = toDocument(cd);
+    if (readOnly) {
+      return;
+    }
     if (cd.getChange().getStatus().isOpen()) {
       closedIndex.delete(id);
       openIndex.insert(doc);
@@ -121,6 +123,9 @@ public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
   public void replace(ChangeData cd) throws IOException {
     Term id = idTerm(cd);
     Document doc = toDocument(cd);
+    if (readOnly) {
+      return;
+    }
     if (cd.getChange().getStatus().isOpen()) {
       closedIndex.delete(id);
       openIndex.replace(id, doc);
@@ -133,6 +138,9 @@ public class LuceneChangeIndex implements ChangeIndex, LifecycleListener {
   @Override
   public void delete(ChangeData cd) throws IOException {
     Term id = idTerm(cd);
+    if (readOnly) {
+      return;
+    }
     if (cd.getChange().getStatus().isOpen()) {
       openIndex.delete(id);
     } else {

gerrit-lucene/src/main/java/com/google/gerrit/lucene/LuceneIndexModule.java

@@ -15,20 +15,29 @@
 package com.google.gerrit.lucene;
 
 import com.google.gerrit.lifecycle.LifecycleModule;
+import com.google.gerrit.server.config.SitePaths;
 import com.google.gerrit.server.index.ChangeIndex;
+import com.google.gerrit.server.index.FieldDef.FillArgs;
 import com.google.gerrit.server.index.IndexModule;
+import com.google.inject.Provides;
+import com.google.inject.Singleton;
+
+import java.io.IOException;
 
 public class LuceneIndexModule extends LifecycleModule {
   private final boolean checkVersion;
   private final int threads;
+  private final boolean readOnly;
 
   public LuceneIndexModule() {
-    this(true, 0);
+    this(true, 0, false);
   }
 
-  public LuceneIndexModule(boolean checkVersion, int threads) {
+  public LuceneIndexModule(boolean checkVersion, int threads,
+      boolean readOnly) {
     this.checkVersion = checkVersion;
     this.threads = threads;
+    this.readOnly = readOnly;
   }
 
   @Override
@@ -40,4 +49,11 @@ public class LuceneIndexModule extends LifecycleModule {
       listener().to(IndexVersionCheck.class);
     }
   }
+
+  @Provides
+  @Singleton
+  public LuceneChangeIndex getChangeIndex(SitePaths sitePaths,
+      FillArgs fillArgs) throws IOException {
+    return new LuceneChangeIndex(sitePaths, fillArgs, readOnly);
+  }
 }