HBASE-23264 Resolve a TODO of BucketAllocator: "Why we add the extra … (#801)

Signed-off-by: Viraj Jasani <vjasani@apache.org>

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

@@ -269,8 +269,9 @@ public final class BucketAllocator {
 
   // Default block size in hbase is 64K, so we choose more sizes near 64K, you'd better
   // reset it according to your cluster's block size distribution
+  // The real block size in hfile maybe a little larger than the size we configured ,
+  // so we need add extra 1024 bytes for fit.
   // TODO Support the view of block size distribution statistics
-  // TODO: Why we add the extra 1024 bytes? Slop?
   private static final int DEFAULT_BUCKET_SIZES[] = { 4 * 1024 + 1024, 8 * 1024 + 1024,
       16 * 1024 + 1024, 32 * 1024 + 1024, 40 * 1024 + 1024, 48 * 1024 + 1024,
       56 * 1024 + 1024, 64 * 1024 + 1024, 96 * 1024 + 1024, 128 * 1024 + 1024,