Add soft_rate_limit stats

Summary: This diff adds histogram stats for soft_rate_limit stalls. It also renames the old rate_limit stats to hard_rate_limit.

Test Plan: make -j32 check

Reviewers: dhruba, haobo, MarkCallaghan

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D12021

db/db_impl.cc

@@ -2541,7 +2541,7 @@ Status DBImpl::MakeRoomForWrite(bool force) {
       mutex_.Unlock();
       uint64_t delayed;
       {
-        StopWatch sw(env_, options_.statistics, RATE_LIMIT_DELAY_COUNT);
+        StopWatch sw(env_, options_.statistics, HARD_RATE_LIMIT_DELAY_COUNT);
         env_->SleepForMicroseconds(1000);
         delayed = sw.ElapsedMicros();
       }
@@ -2567,11 +2567,15 @@ Status DBImpl::MakeRoomForWrite(bool force) {
       // Delay a write when the compaction score for any level is too large.
       // TODO: add statistics
       mutex_.Unlock();
-      env_->SleepForMicroseconds(SlowdownAmount(
-        score,
-        options_.soft_rate_limit,
-        options_.hard_rate_limit)
-      );
+      {
+        StopWatch sw(env_, options_.statistics, SOFT_RATE_LIMIT_DELAY_COUNT);
+        env_->SleepForMicroseconds(SlowdownAmount(
+          score,
+          options_.soft_rate_limit,
+          options_.hard_rate_limit)
+        );
+        rate_limit_delay_millis += sw.ElapsedMicros();
+      }
       allow_soft_rate_limit_delay = false;
       mutex_.Lock();
     } else {

include/leveldb/statistics.h

@@ -113,8 +113,9 @@ enum Histograms {
   STALL_L0_SLOWDOWN_COUNT = 12,
   STALL_MEMTABLE_COMPACTION_COUNT = 13,
   STALL_L0_NUM_FILES_COUNT = 14,
-  RATE_LIMIT_DELAY_COUNT = 15,
-  HISTOGRAM_ENUM_MAX = 16
+  HARD_RATE_LIMIT_DELAY_COUNT = 15,
+  SOFT_RATE_LIMIT_DELAY_COUNT = 16,
+  HISTOGRAM_ENUM_MAX = 17
 };
 
 const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
@@ -133,7 +134,8 @@ const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
   { STALL_L0_SLOWDOWN_COUNT, "rocksdb.l0.slowdown.count"},
   { STALL_MEMTABLE_COMPACTION_COUNT, "rocksdb.memtable.compaction.count"},
   { STALL_L0_NUM_FILES_COUNT, "rocksdb.num.files.stall.count"},
-  { RATE_LIMIT_DELAY_COUNT, "rocksdb.rate.limit.delay.count"}
+  { HARD_RATE_LIMIT_DELAY_COUNT, "rocksdb.hard.rate.limit.delay.count"},
+  { SOFT_RATE_LIMIT_DELAY_COUNT, "rocksdb.soft.rate.limit.delay.count"}
 };
 
 struct HistogramData {