Index: lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java	(revision 1445352)
+++ lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java	(working copy)
@@ -520,7 +520,7 @@
       }
 
       if (infoStream.isEnabled("DWPT")) {
-        final double newSegmentSize = segmentInfo.sizeInBytes()/1024./1024.;
+        final double newSegmentSize = segmentInfoPerCommit.sizeInBytes()/1024./1024.;
         infoStream.message("DWPT", "flushed: segment=" + segmentInfo.name + 
                 " ramUsed=" + nf.format(startMBUsed) + " MB" +
                 " newFlushedSize(includes docstores)=" + nf.format(newSegmentSize) + " MB" +
@@ -557,7 +557,7 @@
 
     IndexWriter.setDiagnostics(newSegment.info, "flush");
     
-    IOContext context = new IOContext(new FlushInfo(newSegment.info.getDocCount(), newSegment.info.sizeInBytes()));
+    IOContext context = new IOContext(new FlushInfo(newSegment.info.getDocCount(), newSegment.sizeInBytes()));
 
     boolean success = false;
     try {
Index: lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(revision 1445352)
+++ lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -2301,7 +2301,7 @@
               infoStream.message("IW", "addIndexes: process segment origName=" + info.info.name + " newName=" + newSegName + " info=" + info);
             }
 
-            IOContext context = new IOContext(new MergeInfo(info.info.getDocCount(), info.info.sizeInBytes(), true, -1));
+            IOContext context = new IOContext(new MergeInfo(info.info.getDocCount(), info.sizeInBytes(), true, -1));
 
             for(FieldInfo fi : getFieldInfos(info.info)) {
               globalFieldNumberMap.addOrGet(fi.name, fi.number, fi.getDocValuesType());
@@ -3458,7 +3458,7 @@
         final int delCount = numDeletedDocs(info);
         assert delCount <= info.info.getDocCount();
         final double delRatio = ((double) delCount)/info.info.getDocCount();
-        merge.estimatedMergeBytes += info.info.sizeInBytes() * (1.0 - delRatio);
+        merge.estimatedMergeBytes += info.sizeInBytes() * (1.0 - delRatio);
       }
     }
   }
@@ -3759,7 +3759,7 @@
       // lost... 
 
       if (infoStream.isEnabled("IW")) {
-        infoStream.message("IW", String.format(Locale.ROOT, "merged segment size=%.3f MB vs estimate=%.3f MB", merge.info.info.sizeInBytes()/1024./1024., merge.estimatedMergeBytes/1024/1024.));
+        infoStream.message("IW", String.format(Locale.ROOT, "merged segment size=%.3f MB vs estimate=%.3f MB", merge.info.sizeInBytes()/1024./1024., merge.estimatedMergeBytes/1024/1024.));
       }
 
       final IndexReaderWarmer mergedSegmentWarmer = config.getMergedSegmentWarmer();
Index: lucene/core/src/java/org/apache/lucene/index/MergePolicy.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/MergePolicy.java	(revision 1445352)
+++ lucene/core/src/java/org/apache/lucene/index/MergePolicy.java	(working copy)
@@ -192,7 +192,7 @@
     public long totalBytesSize() throws IOException {
       long total = 0;
       for (SegmentInfoPerCommit info : segments) {
-        total += info.info.sizeInBytes();
+        total += info.sizeInBytes();
       }
       return total;
     }
Index: lucene/core/src/java/org/apache/lucene/index/SegmentInfo.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/SegmentInfo.java	(revision 1445352)
+++ lucene/core/src/java/org/apache/lucene/index/SegmentInfo.java	(working copy)
@@ -18,7 +18,6 @@
  */
 
 
-import java.io.IOException;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -57,8 +56,6 @@
 
   private boolean isCompoundFile;
 
-  private volatile long sizeInBytes = -1;         // total byte size of all files (computed on demand)
-
   private Codec codec;
 
   private Map<String,String> diagnostics;
@@ -101,23 +98,6 @@
   }
 
   /**
-   * Returns total size in bytes of all of files used by
-   * this segment.  Note that this will not include any live
-   * docs for the segment; to include that use {@link
-   * SegmentInfoPerCommit#sizeInBytes()} instead.
-   */
-  public long sizeInBytes() throws IOException {
-    if (sizeInBytes == -1) {
-      long sum = 0;
-      for (final String fileName : files()) {
-        sum += dir.fileLength(fileName);
-      }
-      sizeInBytes = sum;
-    }
-    return sizeInBytes;
-  }
-
-  /**
    * Mark whether this segment is stored as a compound file.
    *
    * @param isCompoundFile true if this is a compound file;
@@ -254,7 +234,6 @@
   public void setFiles(Set<String> files) {
     checkFileNames(files);
     setFiles = files;
-    sizeInBytes = -1;
   }
 
   /** Add these files to the set of files written for this
@@ -262,7 +241,6 @@
   public void addFiles(Collection<String> files) {
     checkFileNames(files);
     setFiles.addAll(files);
-    sizeInBytes = -1;
   }
 
   /** Add this file to the set of files written for this
@@ -270,7 +248,6 @@
   public void addFile(String file) {
     checkFileNames(Collections.singleton(file));
     setFiles.add(file);
-    sizeInBytes = -1;
   }
   
   private void checkFileNames(Collection<String> files) {
Index: lucene/core/src/java/org/apache/lucene/index/TieredMergePolicy.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/TieredMergePolicy.java	(revision 1445352)
+++ lucene/core/src/java/org/apache/lucene/index/TieredMergePolicy.java	(working copy)
@@ -374,7 +374,7 @@
       for(int idx = tooBigCount; idx<infosSorted.size(); idx++) {
         final SegmentInfoPerCommit info = infosSorted.get(idx);
         if (merging.contains(info)) {
-          mergingBytes += info.info.sizeInBytes();
+          mergingBytes += info.sizeInBytes();
         } else if (!toBeMerged.contains(info)) {
           eligible.add(info);
         }
@@ -470,7 +470,7 @@
       final long segBytes = size(info);
       totAfterMergeBytes += segBytes;
       totAfterMergeBytesFloored += floorSize(segBytes);
-      totBeforeMergeBytes += info.info.sizeInBytes();
+      totBeforeMergeBytes += info.sizeInBytes();
     }
 
     // Measure "skew" of the merge, which can range
@@ -670,7 +670,7 @@
 
   // Segment size in bytes, pro-rated by % deleted
   private long size(SegmentInfoPerCommit info) throws IOException {
-    final long byteSize = info.info.sizeInBytes();    
+    final long byteSize = info.sizeInBytes();    
     final int delCount = writer.get().numDeletedDocs(info);
     final double delRatio = (info.info.getDocCount() <= 0 ? 0.0f : ((double)delCount / (double)info.info.getDocCount()));    
     assert delRatio <= 1.0;