optimize checksum computation to make sure we only work on buffers and no on single bytes

src/main/java/org/apache/lucene/store/OpenBufferedIndexOutput.java

@@ -0,0 +1,151 @@
+package org.apache.lucene.store;
+
+import java.io.IOException;
+
+/**
+ * Exactly the same as Lucene {@link BufferedIndexOutput} but with the ability to set the buffer size
+ */
+// LUCENE MONITOR
+public abstract class OpenBufferedIndexOutput extends IndexOutput {
+
+    public static final int DEFAULT_BUFFER_SIZE = BufferedIndexOutput.BUFFER_SIZE;
+
+    final int BUFFER_SIZE;
+
+    private final byte[] buffer;
+    private long bufferStart = 0;           // position in file of buffer
+    private int bufferPosition = 0;         // position in buffer
+
+    protected OpenBufferedIndexOutput(int BUFFER_SIZE) {
+        this.BUFFER_SIZE = BUFFER_SIZE;
+        this.buffer = new byte[BUFFER_SIZE];
+    }
+
+    /**
+     * Writes a single byte.
+     *
+     * @see IndexInput#readByte()
+     */
+    @Override
+    public void writeByte(byte b) throws IOException {
+        if (bufferPosition >= BUFFER_SIZE)
+            flush();
+        buffer[bufferPosition++] = b;
+    }
+
+    /**
+     * Writes an array of bytes.
+     *
+     * @param b      the bytes to write
+     * @param length the number of bytes to write
+     * @see IndexInput#readBytes(byte[], int, int)
+     */
+    @Override
+    public void writeBytes(byte[] b, int offset, int length) throws IOException {
+        int bytesLeft = BUFFER_SIZE - bufferPosition;
+        // is there enough space in the buffer?
+        if (bytesLeft >= length) {
+            // we add the data to the end of the buffer
+            System.arraycopy(b, offset, buffer, bufferPosition, length);
+            bufferPosition += length;
+            // if the buffer is full, flush it
+            if (BUFFER_SIZE - bufferPosition == 0)
+                flush();
+        } else {
+            // is data larger then buffer?
+            if (length > BUFFER_SIZE) {
+                // we flush the buffer
+                if (bufferPosition > 0)
+                    flush();
+                // and write data at once
+                flushBuffer(b, offset, length);
+                bufferStart += length;
+            } else {
+                // we fill/flush the buffer (until the input is written)
+                int pos = 0; // position in the input data
+                int pieceLength;
+                while (pos < length) {
+                    pieceLength = (length - pos < bytesLeft) ? length - pos : bytesLeft;
+                    System.arraycopy(b, pos + offset, buffer, bufferPosition, pieceLength);
+                    pos += pieceLength;
+                    bufferPosition += pieceLength;
+                    // if the buffer is full, flush it
+                    bytesLeft = BUFFER_SIZE - bufferPosition;
+                    if (bytesLeft == 0) {
+                        flush();
+                        bytesLeft = BUFFER_SIZE;
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Forces any buffered output to be written.
+     */
+    @Override
+    public void flush() throws IOException {
+        flushBuffer(buffer, bufferPosition);
+        bufferStart += bufferPosition;
+        bufferPosition = 0;
+    }
+
+    /**
+     * Expert: implements buffer write.  Writes bytes at the current position in
+     * the output.
+     *
+     * @param b   the bytes to write
+     * @param len the number of bytes to write
+     */
+    private void flushBuffer(byte[] b, int len) throws IOException {
+        flushBuffer(b, 0, len);
+    }
+
+    /**
+     * Expert: implements buffer write.  Writes bytes at the current position in
+     * the output.
+     *
+     * @param b      the bytes to write
+     * @param offset the offset in the byte array
+     * @param len    the number of bytes to write
+     */
+    protected abstract void flushBuffer(byte[] b, int offset, int len) throws IOException;
+
+    /**
+     * Closes this stream to further operations.
+     */
+    @Override
+    public void close() throws IOException {
+        flush();
+    }
+
+    /**
+     * Returns the current position in this file, where the next write will
+     * occur.
+     *
+     * @see #seek(long)
+     */
+    @Override
+    public long getFilePointer() {
+        return bufferStart + bufferPosition;
+    }
+
+    /**
+     * Sets current position in this file, where the next write will occur.
+     *
+     * @see #getFilePointer()
+     */
+    @Override
+    public void seek(long pos) throws IOException {
+        flush();
+        bufferStart = pos;
+    }
+
+    /**
+     * The number of bytes in the file.
+     */
+    @Override
+    public abstract long length() throws IOException;
+
+
+}

src/main/java/org/elasticsearch/index/store/Store.java

@@ -524,7 +524,7 @@ public class Store extends AbstractIndexShardComponent {
         }
     }
 
-    class StoreIndexOutput extends IndexOutput {
+    class StoreIndexOutput extends OpenBufferedIndexOutput {
 
         private final StoreFileMetaData metaData;
 
@@ -535,6 +535,9 @@ public class Store extends AbstractIndexShardComponent {
         private final Checksum digest;
 
         StoreIndexOutput(StoreFileMetaData metaData, IndexOutput delegate, String name, boolean computeChecksum) {
+            // we add 8 to be bigger than the default BufferIndexOutput buffer size so any flush will go directly
+            // to the output without being copied over to the delegate buffer
+            super(OpenBufferedIndexOutput.DEFAULT_BUFFER_SIZE + 64);
             this.metaData = metaData;
             this.delegate = delegate;
             this.name = name;
@@ -559,6 +562,7 @@ public class Store extends AbstractIndexShardComponent {
 
         @Override
         public void close() throws IOException {
+            super.close();
             delegate.close();
             String checksum = null;
             if (digest != null) {
@@ -572,18 +576,10 @@ public class Store extends AbstractIndexShardComponent {
         }
 
         @Override
-        public void writeByte(byte b) throws IOException {
+        protected void flushBuffer(byte[] b, int offset, int len) throws IOException {
-            delegate.writeByte(b);
+            delegate.writeBytes(b, offset, len);
             if (digest != null) {
-                digest.update(b);
+                digest.update(b, offset, len);
-            }
-        }
-
-        @Override
-        public void writeBytes(byte[] b, int offset, int length) throws IOException {
-            delegate.writeBytes(b, offset, length);
-            if (digest != null) {
-                digest.update(b, offset, length);
             }
         }
 
@@ -594,19 +590,16 @@ public class Store extends AbstractIndexShardComponent {
 
         @Override
         public void flush() throws IOException {
+            super.flush();
             delegate.flush();
         }
 
-        @Override
-        public long getFilePointer() {
-            return delegate.getFilePointer();
-        }
-
         @Override
         public void seek(long pos) throws IOException {
             // seek might be called on files, which means that the checksum is not file checksum
             // but a checksum of the bytes written to this stream, which is the same for each
             // type of file in lucene
+            super.seek(pos);
             delegate.seek(pos);
         }
 
@@ -619,10 +612,5 @@ public class Store extends AbstractIndexShardComponent {
         public void setLength(long length) throws IOException {
             delegate.setLength(length);
         }
-
-        @Override
-        public void writeStringStringMap(Map<String, String> map) throws IOException {
-            delegate.writeStringStringMap(map);
-        }
     }
 }