This closes #1324

artemis-server/src/main/java/org/apache/activemq/artemis/core/paging/impl/Page.java

@@ -16,18 +16,26 @@
  */
 package org.apache.activemq.artemis.core.paging.impl;
 
+import java.io.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import io.netty.util.internal.PlatformDependent;
 import org.apache.activemq.artemis.api.core.ActiveMQBuffer;
 import org.apache.activemq.artemis.api.core.ActiveMQBuffers;
 import org.apache.activemq.artemis.api.core.ICoreMessage;
 import org.apache.activemq.artemis.api.core.SimpleString;
 import org.apache.activemq.artemis.core.io.SequentialFile;
 import org.apache.activemq.artemis.core.io.SequentialFileFactory;
+import org.apache.activemq.artemis.core.io.mapped.MappedSequentialFileFactory;
+import org.apache.activemq.artemis.core.io.nio.NIOSequentialFileFactory;
 import org.apache.activemq.artemis.core.paging.PagedMessage;
 import org.apache.activemq.artemis.core.paging.cursor.LivePageCache;
 import org.apache.activemq.artemis.core.paging.cursor.PageSubscriptionCounter;
@@ -78,6 +86,8 @@ public final class Page implements Comparable<Page> {
     */
    private Set<PageSubscriptionCounter> pendingCounters;
 
+   private boolean canBeMapped;
+
    public Page(final SimpleString storeName,
                final StorageManager storageManager,
                final SequentialFileFactory factory,
@@ -88,6 +98,7 @@ public final class Page implements Comparable<Page> {
       fileFactory = factory;
       this.storageManager = storageManager;
       this.storeName = storeName;
+      this.canBeMapped = fileFactory instanceof NIOSequentialFileFactory || fileFactory instanceof MappedSequentialFileFactory;
    }
 
    public int getPageId() {
@@ -107,9 +118,22 @@ public final class Page implements Comparable<Page> {
          throw ActiveMQMessageBundle.BUNDLE.invalidPageIO();
       }
 
-      ArrayList<PagedMessage> messages = new ArrayList<>();
+      final List<PagedMessage> messages = new ArrayList<>();
 
-      size.set((int) file.size());
+      size.lazySet((int) file.size());
+
+      if (this.canBeMapped) {
+         readFromMapped(storage, messages);
+      } else {
+         readFromSequentialFile(storage, messages);
+      }
+
+      numberOfMessages.lazySet(messages.size());
+
+      return messages;
+   }
+
+   private void readFromSequentialFile(StorageManager storage, List<PagedMessage> messages) throws Exception {
       // Using direct buffer, as described on https://jira.jboss.org/browse/HORNETQ-467
       ByteBuffer directBuffer = storage.allocateDirectBuffer((int) file.size());
       ActiveMQBuffer fileBuffer = null;
@@ -122,7 +146,40 @@ public final class Page implements Comparable<Page> {
 
          fileBuffer = ActiveMQBuffers.wrappedBuffer(directBuffer);
          fileBuffer.writerIndex(fileBuffer.capacity());
+         read(storage, fileBuffer, messages);
+      } finally {
+         if (fileBuffer != null) {
+            fileBuffer.byteBuf().unwrap().release();
+         }
+         storage.freeDirectBuffer(directBuffer);
+      }
+   }
 
+   private static MappedByteBuffer mapFileForRead(File file, int fileSize) {
+      try (RandomAccessFile raf = new RandomAccessFile(file, "rw");
+           FileChannel channel = raf.getChannel()) {
+         return channel.map(FileChannel.MapMode.READ_ONLY, 0, fileSize);
+      } catch (Exception e) {
+         throw new IllegalStateException(e);
+      }
+   }
+
+   private int readFromMapped(StorageManager storage, List<PagedMessage> messages) throws IOException {
+      file.position(0);
+      //use a readonly mapped view of the file
+      final MappedByteBuffer mappedByteBuffer = mapFileForRead(this.file.getJavaFile(), size.get());
+      try {
+         final ActiveMQBuffer fileBuffer = ActiveMQBuffers.wrappedBuffer(mappedByteBuffer);
+         fileBuffer.writerIndex(fileBuffer.capacity());
+         return read(storage, fileBuffer, messages);
+      } finally {
+         //unmap the file after read it to avoid GC to take care of it
+         PlatformDependent.freeDirectBuffer(mappedByteBuffer);
+      }
+   }
+
+   private int read(StorageManager storage, ActiveMQBuffer fileBuffer, List<PagedMessage> messages) {
+      int readMessages = 0;
       while (fileBuffer.readable()) {
          final int position = fileBuffer.readerIndex();
 
@@ -146,6 +203,7 @@ public final class Page implements Comparable<Page> {
                   if (logger.isTraceEnabled()) {
                      logger.trace("Reading message " + msg + " on pageId=" + this.pageId + " for address=" + storeName);
                   }
+                  readMessages++;
                   messages.add(msg);
                } else {
                   markFileAsSuspect(file.getFileName(), position, messages.size());
@@ -157,16 +215,7 @@ public final class Page implements Comparable<Page> {
             break;
          }
       }
-      } finally {
-         if (fileBuffer != null) {
-            fileBuffer.byteBuf().unwrap().release();
-         }
-         storage.freeDirectBuffer(directBuffer);
-      }
-
-      numberOfMessages.set(messages.size());
-
-      return messages;
+      return readMessages;
    }
 
    public synchronized void write(final PagedMessage message) throws Exception {