Add counters for L0 stall while L0-L1 compaction is taking place

Summary:
Although there are currently counters to keep track of the
stall caused by having too many L0 files, there is no distinction as
to whether when that stall occurs either (A) L0-L1 compaction is taking
place to try and mitigate it, or (B) no L0-L1 compaction has been scheduled
at the moment. This diff adds a counter for (A) so that the nature of L0
stalls can be better understood.

Test Plan: make all && make check

Reviewers: sdong, igor, anthony, noetzli, yhchiang

Reviewed By: yhchiang

Subscribers: MarkCallaghan, dhruba

Differential Revision: https://reviews.facebook.net/D46749

db/column_family.cc

@@ -446,7 +446,11 @@ void ColumnFamilyData::RecalculateWriteStallConditions(
     } else if (vstorage->l0_delay_trigger_count() >=
                mutable_cf_options.level0_stop_writes_trigger) {
       write_controller_token_ = write_controller->GetStopToken();
-      internal_stats_->AddCFStats(InternalStats::LEVEL0_NUM_FILES, 1);
+      internal_stats_->AddCFStats(InternalStats::LEVEL0_NUM_FILES_TOTAL, 1);
+      if (compaction_picker_->IsLevel0CompactionInProgress()) {
+        internal_stats_->AddCFStats(
+            InternalStats::LEVEL0_NUM_FILES_WITH_COMPACTION, 1);
+      }
       Log(InfoLogLevel::WARN_LEVEL, ioptions_.info_log,
           "[%s] Stopping writes because we have %d level-0 files",
           name_.c_str(), vstorage->l0_delay_trigger_count());
@@ -454,7 +458,11 @@ void ColumnFamilyData::RecalculateWriteStallConditions(
                vstorage->l0_delay_trigger_count() >=
                    mutable_cf_options.level0_slowdown_writes_trigger) {
       write_controller_token_ = write_controller->GetDelayToken();
-      internal_stats_->AddCFStats(InternalStats::LEVEL0_SLOWDOWN, 1);
+      internal_stats_->AddCFStats(InternalStats::LEVEL0_SLOWDOWN_TOTAL, 1);
+      if (compaction_picker_->IsLevel0CompactionInProgress()) {
+        internal_stats_->AddCFStats(
+            InternalStats::LEVEL0_SLOWDOWN_WITH_COMPACTION, 1);
+      }
       Log(InfoLogLevel::WARN_LEVEL, ioptions_.info_log,
           "[%s] Stalling writes because we have %d level-0 files",
           name_.c_str(), vstorage->l0_delay_trigger_count());

db/compaction_job.cc

@@ -316,6 +316,8 @@ void CompactionJob::Prepare() {
       Slice* end = i == boundaries_.size() ? nullptr : &boundaries_[i];
       compact_->sub_compact_states.emplace_back(c, start, end, sizes_[i]);
     }
+    MeasureTime(stats_, NUM_SUBCOMPACTIONS_SCHEDULED,
+                compact_->sub_compact_states.size());
   } else {
     compact_->sub_compact_states.emplace_back(c, nullptr, nullptr);
   }

db/compaction_picker.h

@@ -110,6 +110,11 @@ class CompactionPicker {
   // overlapping.
   bool IsInputNonOverlapping(Compaction* c);
 
+  // Is there currently a compaction involving level 0 taking place
+  bool IsLevel0CompactionInProgress() const {
+    return !level0_compactions_in_progress_.empty();
+  }
+
  protected:
   int NumberLevels() const { return ioptions_.num_levels; }
 

db/internal_stats.cc

@@ -669,12 +669,11 @@ void InternalStats::DumpCFStats(std::string* value) {
     total_files += files;
     total_files_being_compacted += files_being_compacted[level];
     if (comp_stats_[level].micros > 0 || files > 0) {
-      uint64_t stalls = level == 0 ?
-        (cf_stats_count_[LEVEL0_SLOWDOWN] +
-         cf_stats_count_[LEVEL0_NUM_FILES] +
-         cf_stats_count_[MEMTABLE_COMPACTION])
-        : (stall_leveln_slowdown_count_soft_[level] +
-           stall_leveln_slowdown_count_hard_[level]);
+      uint64_t stalls = level == 0 ? (cf_stats_count_[LEVEL0_SLOWDOWN_TOTAL] +
+                                      cf_stats_count_[LEVEL0_NUM_FILES_TOTAL] +
+                                      cf_stats_count_[MEMTABLE_COMPACTION])
+                                   : (stall_leveln_slowdown_count_soft_[level] +
+                                      stall_leveln_slowdown_count_hard_[level]);
 
       stats_sum.Add(comp_stats_[level]);
       total_file_size += vstorage->NumLevelBytes(level);
@@ -718,11 +717,16 @@ void InternalStats::DumpCFStats(std::string* value) {
 
   snprintf(buf, sizeof(buf),
            "Stalls(count): %" PRIu64 " level0_slowdown, "
-           "%" PRIu64 " level0_numfiles, %" PRIu64 " memtable_compaction, "
+           "%" PRIu64 " level0_slowdown_with_compaction, "
+           "%" PRIu64 " level0_numfiles, "
+           "%" PRIu64 " level0_numfiles_with_compaction, "
+           "%" PRIu64 " memtable_compaction, "
            "%" PRIu64 " leveln_slowdown_soft, "
            "%" PRIu64 " leveln_slowdown_hard\n",
-           cf_stats_count_[LEVEL0_SLOWDOWN],
-           cf_stats_count_[LEVEL0_NUM_FILES],
+           cf_stats_count_[LEVEL0_SLOWDOWN_TOTAL],
+           cf_stats_count_[LEVEL0_SLOWDOWN_WITH_COMPACTION],
+           cf_stats_count_[LEVEL0_NUM_FILES_TOTAL],
+           cf_stats_count_[LEVEL0_NUM_FILES_WITH_COMPACTION],
            cf_stats_count_[MEMTABLE_COMPACTION],
            total_slowdown_count_soft, total_slowdown_count_hard);
   value->append(buf);

db/internal_stats.h

@@ -80,9 +80,11 @@ extern DBPropertyType GetPropertyType(const Slice& property,
 class InternalStats {
  public:
   enum InternalCFStatsType {
-    LEVEL0_SLOWDOWN,
+    LEVEL0_SLOWDOWN_TOTAL,
+    LEVEL0_SLOWDOWN_WITH_COMPACTION,
     MEMTABLE_COMPACTION,
-    LEVEL0_NUM_FILES,
+    LEVEL0_NUM_FILES_TOTAL,
+    LEVEL0_NUM_FILES_WITH_COMPACTION,
     WRITE_STALLS_ENUM_MAX,
     BYTES_FLUSHED,
     INTERNAL_CF_STATS_ENUM_MAX,
@@ -350,9 +352,11 @@ class InternalStats {
 class InternalStats {
  public:
   enum InternalCFStatsType {
-    LEVEL0_SLOWDOWN,
+    LEVEL0_SLOWDOWN_TOTAL,
+    LEVEL0_SLOWDOWN_WITH_COMPACTION,
     MEMTABLE_COMPACTION,
-    LEVEL0_NUM_FILES,
+    LEVEL0_NUM_FILES_TOTAL,
+    LEVEL0_NUM_FILES_WITH_COMPACTION,
     WRITE_STALLS_ENUM_MAX,
     BYTES_FLUSHED,
     INTERNAL_CF_STATS_ENUM_MAX,

include/rocksdb/statistics.h

@@ -271,6 +271,8 @@ enum Histograms : uint32_t {
   DB_SEEK,
   WRITE_STALL,
   SST_READ_MICROS,
+  // The number of subcompactions actually scheduled during a compaction
+  NUM_SUBCOMPACTIONS_SCHEDULED,
   HISTOGRAM_ENUM_MAX,  // TODO(ldemailly): enforce HistogramsNameMap match
 };
 
@@ -297,6 +299,7 @@ const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
     {DB_SEEK, "rocksdb.db.seek.micros"},
     {WRITE_STALL, "rocksdb.db.write.stall"},
     {SST_READ_MICROS, "rocksdb.sst.read.micros"},
+    {NUM_SUBCOMPACTIONS_SCHEDULED, "rocksdb.num.subcompactions.scheduled"},
 };
 
 struct HistogramData {