output perf_context in db_bench readrandom

Summary:
Add helper function to print perf context data in db_bench if enabled.
I didn't find any code that actually exports perf context data. Not sure
if I missed anything

Test Plan: ran db_bench

Reviewers: haobo, sdong, igor

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16575

db/db_bench.cc

@@ -1994,7 +1994,12 @@ class Benchmark {
     char msg[100];
     snprintf(msg, sizeof(msg), "(%" PRIu64 " of %" PRIu64 " found)",
              found, reads_);
+
     thread->stats.AddMessage(msg);
+
+    if (FLAGS_perf_level > 0) {
+      thread->stats.AddMessage(perf_context.ToString());
+    }
   }
 
   void PrefixScanRandom(ThreadState* thread) {

include/rocksdb/perf_context.h

@@ -7,6 +7,7 @@
 #define STORAGE_ROCKSDB_INCLUDE_PERF_CONTEXT_H
 
 #include <stdint.h>
+#include <string>
 
 namespace rocksdb {
 
@@ -26,6 +27,8 @@ struct PerfContext {
 
   void Reset(); // reset all performance counters to zero
 
+  std::string ToString() const;
+
   uint64_t user_key_comparison_count; // total number of user key comparisons
   uint64_t block_cache_hit_count;     // total number of block cache hits
   uint64_t block_read_count;          // total number of block reads (with IO)

util/perf_context.cc

@@ -3,6 +3,8 @@
 //  LICENSE file in the root directory of this source tree. An additional grant
 //  of patent rights can be found in the PATENTS file in the same directory.
 //
+
+#include <sstream>
 #include "util/perf_context_imp.h"
 
 namespace rocksdb {
@@ -38,6 +40,35 @@ void PerfContext::Reset() {
   write_memtable_time = 0;
 }
 
+#define OUTPUT(counter) #counter << " = " << counter << ", "
+
+std::string PerfContext::ToString() const {
+  std::ostringstream ss;
+  ss << OUTPUT(user_key_comparison_count)
+     << OUTPUT(block_cache_hit_count)
+     << OUTPUT(block_read_count)
+     << OUTPUT(block_read_byte)
+     << OUTPUT(block_read_time)
+     << OUTPUT(block_checksum_time)
+     << OUTPUT(block_decompress_time)
+     << OUTPUT(internal_key_skipped_count)
+     << OUTPUT(internal_delete_skipped_count)
+     << OUTPUT(write_wal_time)
+     << OUTPUT(get_snapshot_time)
+     << OUTPUT(get_from_memtable_time)
+     << OUTPUT(get_from_memtable_count)
+     << OUTPUT(get_post_process_time)
+     << OUTPUT(get_from_output_files_time)
+     << OUTPUT(seek_child_seek_time)
+     << OUTPUT(seek_child_seek_count)
+     << OUTPUT(seek_min_heap_time)
+     << OUTPUT(seek_internal_seek_time)
+     << OUTPUT(find_next_user_entry_time)
+     << OUTPUT(write_pre_and_post_process_time)
+     << OUTPUT(write_memtable_time);
+  return ss.str();
+}
+
 __thread PerfContext perf_context;
 
 }