add options.block_restart_interval in db_bench

Summary:
  Add block_restart_interval in db_bench, default value 16

Test Plan:
  make

Reviewers: sdong

Reviewed By: sdong

Differential Revision: https://reviews.facebook.net/D20331

db/db_bench.cc

@@ -242,6 +242,10 @@ DEFINE_int64(cache_size, -1, "Number of bytes to use as a cache of uncompressed"
 DEFINE_int32(block_size, rocksdb::Options().block_size,
              "Number of bytes in a block.");
 
+DEFINE_int32(block_restart_interval, rocksdb::Options().block_restart_interval,
+             "Number of keys between restart points "
+             "for delta encoding of keys.");
+
 DEFINE_int64(compressed_cache_size, -1,
              "Number of bytes to use as a cache of compressed data.");
 
@@ -1626,6 +1630,7 @@ class Benchmark {
     options.max_background_flushes = FLAGS_max_background_flushes;
     options.compaction_style = FLAGS_compaction_style_e;
     options.block_size = FLAGS_block_size;
+    options.block_restart_interval = FLAGS_block_restart_interval;
     options.filter_policy = filter_policy_;
     if (FLAGS_prefix_size != 0) {
       options.prefix_extractor.reset(