Improve BufferedIndexInput.readBytes() performance: LUCENE-695

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@468172 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -185,6 +185,10 @@ Optimizations
   9. LUCENE-365: DisjunctionSumScorer performance increase of ~30%. Speeds up
      queries with optional clauses. (Paul Elschot via Yonik Seeley)
 
+ 10. LUCENE-695: Optimized BufferedIndexInput.readBytes() for medium size buffers,
+     which will speed up merging and retrieving binary and compressed fields.
+     (Nadav Har'El via Yonik Seeley)
+
 Test Cases
   1. Added TestTermScorer.java (Grant Ingersoll)
 

src/java/org/apache/lucene/store/BufferedIndexInput.java

@@ -34,19 +34,47 @@ public abstract class BufferedIndexInput extends IndexInput {
     return buffer[bufferPosition++];
   }
 
-  public void readBytes(byte[] b, int offset, int len)
-       throws IOException {
-    if (len < BUFFER_SIZE) {
-      for (int i = 0; i < len; i++)		  // read byte-by-byte
-	b[i + offset] = (byte)readByte();
-    } else {					  // read all-at-once
-      long start = getFilePointer();
-      seekInternal(start);
-      readInternal(b, offset, len);
-
-      bufferStart = start + len;		  // adjust stream variables
-      bufferPosition = 0;
-      bufferLength = 0;				  // trigger refill() on read
+  public void readBytes(byte[] b, int offset, int len) throws IOException {
+    if(len <= (bufferLength-bufferPosition)){
+      // the buffer contains enough data to satistfy this request
+      if(len>0) // to allow b to be null if len is 0...
+    	  System.arraycopy(buffer, bufferPosition, b, offset, len);
+      bufferPosition+=len;
+    } else {
+      // the buffer does not have enough data. First serve all we've got.
+      int available = bufferLength - bufferPosition;
+      if(available > 0){
+        System.arraycopy(buffer, bufferPosition, b, offset, available);
+        offset += available;
+        len -= available;
+        bufferPosition += available;
+      }
+      // and now, read the remaining 'len' bytes:
+      if(len<BUFFER_SIZE){
+        // If the amount left to read is small enough, do it in the usual
+        // buffered way: fill the buffer and copy from it:
+        refill();
+        if(bufferLength<len){
+          // Throw an exception when refill() could not read len bytes:
+          System.arraycopy(buffer, 0, b, offset, bufferLength);
+          throw new IOException("read past EOF");
+        } else {
+          System.arraycopy(buffer, 0, b, offset, len);
+          bufferPosition=len;
+        }
+      } else {
+        // The amount left to read is larger than the buffer - there's no
+        // performance reason not to read it all at once. Note that unlike
+        // the previous code of this function, there is no need to do a seek
+        // here, because there's no need to reread what we had in the buffer.
+    	long after = bufferStart+bufferPosition+len;
+    	if(after > length())
+            throw new IOException("read past EOF");  		
+        readInternal(b, offset, len);
+    	bufferStart = after; 
+        bufferPosition = 0;
+        bufferLength = 0;                    // trigger refill() on read
+      }
     }
   }