Index: src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentTracker.java
===================================================================
--- src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentTracker.java	(revision 1698136)
+++ src/main/java/org/apache/jackrabbit/oak/plugins/segment/SegmentTracker.java	(working copy)
@@ -23,6 +23,7 @@
 import java.security.SecureRandom;
 import java.util.Queue;
 import java.util.Set;
+import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -37,6 +38,8 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.cache.Weigher;
+
 /**
  * Tracker of references to segment identifiers and segment instances
  * that are currently kept in memory.
@@ -106,6 +109,13 @@
      */
     private final CacheLIRS<SegmentId, Segment> segmentCache;
 
+    private final static Weigher<SegmentId, Segment> segmentCacheWeigher = new Weigher<SegmentId, Segment>() {
+        @Override
+        public int weigh(SegmentId key, Segment value) {
+            return value.size();
+        }
+    };
+
     public SegmentTracker(SegmentStore store, int cacheSizeMB,
             SegmentVersion version) {
         for (int i = 0; i < tables.length; i++) {
@@ -128,6 +138,7 @@
             .module("SegmentTracker")
             .maximumSize((int) Math.min(Integer.MAX_VALUE, cacheSizeMB * MB))
             .averageWeight(Segment.MAX_SEGMENT_SIZE/2)
+            .weigher(segmentCacheWeigher)
             .evictionCallback(new EvictionCallback<SegmentId, Segment>() {
                 @Override
                 public void evicted(SegmentId segmentId, Segment segment) {
@@ -149,7 +160,8 @@
 
     @Nonnull
     public CacheStats getSegmentCacheStats() {
-        return new CacheStats(segmentCache, "Segment Cache", null, -1);
+        return new CacheStats(segmentCache, "Segment Cache",
+                segmentCacheWeigher, segmentCache.getMaxMemory());
     }
 
     @CheckForNull
@@ -192,25 +204,47 @@
      * @return  segment with the given {@code id} or {@code null} if not in the cache
      */
     Segment getCachedSegment(SegmentId id) {
+        return segmentCache.getIfPresent(id);
+    }
+
+    private Callable<Segment> loader(final SegmentId id) {
+        return new Callable<Segment>() {
+            @Override
+            public Segment call() throws Exception {
+                return loadSegmentFromStore(id);
+            }
+        };
+    }
+
+    /**
+     * Read a segment from the segment store.
+     * @param id  segment id
+     * @return  segment with the given id
+     * @throws SegmentNotFoundException  if no segment with the given {@code id} exists.
+     */
+    Segment readSegment(SegmentId id) {
         try {
-            return segmentCache.get(id);
+            // TODO should bulk segments go into the cache?
+            Segment s = segmentCache.get(id, loader(id));
+            id.setSegment(s);
+            return s;
         } catch (ExecutionException e) {
-            log.error("Error reading from segment cache", e);
-            return null;
+            if (e.getCause() instanceof SegmentNotFoundException) {
+                throw (SegmentNotFoundException) e.getCause();
+            }
+            throw new SegmentNotFoundException(id, e.getCause());
         }
     }
 
     /**
-     * Read a segment from the underlying segment store.
+     * Performs the actual IO operation to read a segment from the underlying store.
      * @param id  segment id
      * @return  segment with the given id
      * @throws SegmentNotFoundException  if no segment with the given {@code id} exists.
      */
-    Segment readSegment(SegmentId id) {
+    private Segment loadSegmentFromStore(SegmentId id) {
         try {
-            Segment segment = store.readSegment(id);
-            setSegment(id, segment);
-            return segment;
+            return store.readSegment(id);
         } catch (SegmentNotFoundException snfe) {
             long delta = System.currentTimeMillis() - id.getCreationTime();
             log.error("Segment not found: {}. Creation date delta is {} ms.",