HBASE-15640 L1 cache doesn't give fair warning that it is showing partial stats only when it hits limit

hbase-server/src/main/jamon/org/apache/hadoop/hbase/tmpl/regionserver/BlockCacheTmpl.jamon

@@ -305,7 +305,11 @@ are combined counts. Request count is sum of hits and misses.</p>
   }
 </%java>
 <%if cbsbf.isFull() %>
-<p><b>Statistics below is based on sampling first <% cbsbfSnapshot.getMax() %> blocks only</b> (hbase.ui.blockcache.by.file.max)</p> 
+<p>
+<div class="alert alert-danger">
+<strong>The stats below are incomplete!</strong> We ran into our accounting limit of <% cbsbf.getCount() %> blocks. Up the configuration <i>hbase.ui.blockcache.by.file.max</i>.
+</div>
+</p> 
 </%if>
 <table id="blocks_summary" class="table table-striped">
     <tr>

hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockCacheUtil.java

@@ -179,16 +179,22 @@ public class BlockCacheUtil {
     private long size;
     private long dataSize;
     private final long now = System.nanoTime();
+    /**
+     * How many blocks to look at before we give up.
+     * There could be many millions of blocks. We don't want the
+     * ui to freeze while we run through 1B blocks... users will
+     * think hbase dead. UI displays warning in red when stats
+     * are incomplete.
+     */
     private final int max;
-    public static final int DEFAULT_MAX = 100000;
+    public static final int DEFAULT_MAX = 1000000;
- 
+
     CachedBlocksByFile() {
       this(null);
     }
 
     CachedBlocksByFile(final Configuration c) {
-      this.max = c == null? DEFAULT_MAX:
+      this.max = c == null? DEFAULT_MAX: c.getInt("hbase.ui.blockcache.by.file.max", DEFAULT_MAX);
-        c.getInt("hbase.ui.blockcache.by.file.max", DEFAULT_MAX);
     }
 
     /**
@@ -230,7 +236,7 @@ public class BlockCacheUtil {
     public boolean isFull() {
       return this.count >= this.max;
     }
- 
+
     public NavigableMap<String, NavigableSet<CachedBlock>> getCachedBlockStatsByFile() {
       return this.cachedBlockByFile;
     }

hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderV2.java

@@ -195,7 +195,7 @@ public class HFileReaderV2 extends AbstractHFileReader {
             end = getTrailer().getLoadOnOpenDataOffset();
             HFileBlock prevBlock = null;
             if (LOG.isTraceEnabled()) {
-              LOG.trace("Prefetch=" + path.toString() + ", offset=" + offset + ", end=" + end);
+              LOG.trace("Prefetch start " + getPathOffsetEndStr(path, offset, end));
             }
             while (offset < end) {
               if (Thread.interrupted()) {
@@ -213,11 +213,14 @@ public class HFileReaderV2 extends AbstractHFileReader {
           } catch (IOException e) {
             // IOExceptions are probably due to region closes (relocation, etc.)
             if (LOG.isTraceEnabled()) {
-              LOG.trace("Prefetch=" + path.toString() + ", offset=" + offset + ", end=" + end, e);
+              LOG.trace("Prefetch " + getPathOffsetEndStr(path, offset, end), e);
             }
+          } catch (NullPointerException e) {
+            LOG.warn("Stream moved/closed or prefetch cancelled?" +
+                getPathOffsetEndStr(path, offset, end), e);
           } catch (Exception e) {
             // Other exceptions are interesting
-            LOG.warn("Prefetch=" + path.toString() + ", offset=" + offset + ", end=" + end, e);
+            LOG.warn("Prefetch " + getPathOffsetEndStr(path, offset, end), e);
           } finally {
             PrefetchExecutor.complete(path);
           }
@@ -235,6 +238,10 @@ public class HFileReaderV2 extends AbstractHFileReader {
       .build();
   }
 
+  private static String getPathOffsetEndStr(final Path path, final long offset, final long end) {
+    return "path=" + path.toString() + ", offset=" + offset + ", end=" + end;
+  }
+
   /**
    * Create a Scanner on this file. No seeks or reads are done on creation. Call
    * {@link HFileScanner#seekTo(byte[])} to position an start the read. There is