[RocksDB] Expose DBStatistics

Summary: Make Statistics usable by client

Test Plan: make check; db_bench

Reviewers: dhruba

Reviewed By: dhruba

Differential Revision: https://reviews.facebook.net/D10899

db/db_bench.cc

@@ -1817,7 +1817,7 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--statistics=%d%c", &n, &junk) == 1 &&
                (n == 0 || n == 1)) {
       if (n == 1) {
-        dbstats.reset(new leveldb::DBStatistics());
+        dbstats = leveldb::CreateDBStatistics();
         FLAGS_statistics = true;
       }
     } else if (sscanf(argv[i], "--writes=%d%c", &n, &junk) == 1) {

db/db_statistics.h

@@ -8,6 +8,7 @@
 #include <cassert>
 #include <stdlib.h>
 #include <vector>
+#include <memory>
 
 #include "leveldb/statistics.h"
 #include "util/histogram.h"
@@ -48,6 +49,11 @@ class DBStatistics: public Statistics {
   std::vector<Ticker> allTickers_;
   std::vector<HistogramImpl> allHistograms_;
 };
+
+std::shared_ptr<Statistics> CreateDBStatistics() {
+  return std::make_shared<DBStatistics>();
+}
+
 } // namespace leveldb
 
 #endif // LEVELDB_STORAGE_DB_DB_STATISTICS_H_

include/leveldb/statistics.h

@@ -128,6 +128,9 @@ class Statistics {
 
 };
 
+// Create a concrete DBStatistics object
+std::shared_ptr<Statistics> CreateDBStatistics();
+
 // Ease of Use functions
 inline void RecordTick(std::shared_ptr<Statistics> statistics,
                        Tickers ticker,

tools/db_stress.cc

@@ -1081,7 +1081,7 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--statistics=%d%c", &n, &junk) == 1 &&
                (n == 0 || n == 1)) {
       if (n == 1) {
-        dbstats.reset(new leveldb::DBStatistics());
+        dbstats = leveldb::CreateDBStatistics();
       }
     } else if (sscanf(argv[i], "--sync=%d%c", &n, &junk) == 1 &&
                (n == 0 || n == 1)) {