Ensure Correct Behavior of StatsLevel kExceptDetailedTimers and kExceptTimeForMutex (#1308)

* Fix StatsLevel so that kExceptTimeForMutex leaves compression stats enabled and kExceptDetailedTimers disables mutex lock stats. Also change default stats level to kExceptDetailedTimers (disabling both compression and mutex timing).

* Changed order of StatsLevel enum to simplify logic for determining what stats to record.

db/db_test.cc

@@ -4718,7 +4718,7 @@ TEST_F(DBTest, CompressionStatsTest) {
   Options options = CurrentOptions();
   options.compression = type;
   options.statistics = rocksdb::CreateDBStatistics();
-  options.statistics->stats_level_ = StatsLevel::kAll;
+  options.statistics->stats_level_ = StatsLevel::kExceptTimeForMutex;
   DestroyAndReopen(options);
 
   int kNumKeysWritten = 100000;

include/rocksdb/statistics.h

@@ -393,12 +393,12 @@ struct HistogramData {
 };
 
 enum StatsLevel {
+  // Collect all stats except time inside mutex lock AND time spent on
+  // compression.
+  kExceptDetailedTimers,
   // Collect all stats except the counters requiring to get time inside the
   // mutex lock.
   kExceptTimeForMutex,
-  // Collect all stats expect time inside mutex lock AND time spent on
-  // compression
-  kExceptDetailedTimers,
   // Collect all stats, including measuring duration of mutex operations.
   // If getting time is expensive on the platform to run, it can
   // reduce scalability to more threads, especially for writes.
@@ -429,7 +429,7 @@ class Statistics {
     return type < HISTOGRAM_ENUM_MAX;
   }
 
-  StatsLevel stats_level_ = kExceptTimeForMutex;
+  StatsLevel stats_level_ = kExceptDetailedTimers;
 };
 
 // Create a concrete DBStatistics object

util/instrumented_mutex.cc

@@ -11,7 +11,7 @@ namespace rocksdb {
 namespace {
 bool ShouldReportToStats(Env* env, Statistics* stats) {
   return env != nullptr && stats != nullptr &&
-         stats->stats_level_ != kExceptTimeForMutex;
+          stats->stats_level_ > kExceptTimeForMutex;
 }
 }  // namespace