Add a histogram stat for memtable flush

Summary:
Add a new histogram stat called rocksdb.db.flush.micros for memtable
flush
Closes https://github.com/facebook/rocksdb/pull/3269

Differential Revision: D6559496

Pulled By: anand1976

fbshipit-source-id: f5c771ba2568630458751795e8c37a493ff9b14d

db/flush_job.cc

@@ -364,6 +364,7 @@ Status FlushJob::WriteLevel0Table() {
   InternalStats::CompactionStats stats(1);
   stats.micros = db_options_.env->NowMicros() - start_micros;
   stats.bytes_written = meta_.fd.GetFileSize();
+  MeasureTime(stats_, FLUSH_TIME, stats.micros);
   cfd_->internal_stats()->AddCompactionStats(0 /* level */, stats);
   cfd_->internal_stats()->AddCFStats(InternalStats::BYTES_FLUSHED,
                                      meta_.fd.GetFileSize());

db/flush_job_test.cc

@@ -40,6 +40,7 @@ class FlushJobTest : public testing::Test {
     EXPECT_OK(env_->CreateDirIfMissing(dbname_));
     db_options_.db_paths.emplace_back(dbname_,
                                       std::numeric_limits<uint64_t>::max());
+    db_options_.statistics = rocksdb::CreateDBStatistics();
     // TODO(icanadi) Remove this once we mock out VersionSet
     NewDB();
     std::vector<ColumnFamilyDescriptor> column_families;
@@ -138,16 +139,22 @@ TEST_F(FlushJobTest, NonEmpty) {
 
   EventLogger event_logger(db_options_.info_log.get());
   SnapshotChecker* snapshot_checker = nullptr;  // not relavant
-  FlushJob flush_job(
-      dbname_, versions_->GetColumnFamilySet()->GetDefault(), db_options_,
-      *cfd->GetLatestMutableCFOptions(), env_options_, versions_.get(), &mutex_,
-      &shutting_down_, {}, kMaxSequenceNumber, snapshot_checker, &job_context,
-      nullptr, nullptr, nullptr, kNoCompression, nullptr, &event_logger, true);
+  FlushJob flush_job(dbname_, versions_->GetColumnFamilySet()->GetDefault(),
+                     db_options_, *cfd->GetLatestMutableCFOptions(),
+                     env_options_, versions_.get(), &mutex_, &shutting_down_,
+                     {}, kMaxSequenceNumber, snapshot_checker, &job_context,
+                     nullptr, nullptr, nullptr, kNoCompression,
+                     db_options_.statistics.get(), &event_logger, true);
+
+  HistogramData hist;
   FileMetaData fd;
   mutex_.Lock();
   flush_job.PickMemTable();
   ASSERT_OK(flush_job.Run(&fd));
   mutex_.Unlock();
+  db_options_.statistics->histogramData(FLUSH_TIME, &hist);
+  ASSERT_GT(hist.average, 0.0);
+
   ASSERT_EQ(ToString(0), fd.smallest.user_key().ToString());
   ASSERT_EQ("9999a",
             fd.largest.user_key().ToString());  // range tombstone end key
@@ -210,12 +217,15 @@ TEST_F(FlushJobTest, Snapshots) {
                      env_options_, versions_.get(), &mutex_, &shutting_down_,
                      snapshots, kMaxSequenceNumber, snapshot_checker,
                      &job_context, nullptr, nullptr, nullptr, kNoCompression,
-                     nullptr, &event_logger, true);
+                     db_options_.statistics.get(), &event_logger, true);
   mutex_.Lock();
   flush_job.PickMemTable();
   ASSERT_OK(flush_job.Run());
   mutex_.Unlock();
   mock_table_factory_->AssertSingleFile(inserted_keys);
+  HistogramData hist;
+  db_options_.statistics->histogramData(FLUSH_TIME, &hist);
+  ASSERT_GT(hist.average, 0.0);
   job_context.Clean();
 }
 

include/rocksdb/statistics.h

@@ -510,6 +510,8 @@ enum Histograms : uint32_t {
   BLOB_DB_COMPRESSION_MICROS,
   // BlobDB decompression time.
   BLOB_DB_DECOMPRESSION_MICROS,
+  // Time spent flushing memtable to disk
+  FLUSH_TIME,
 
   HISTOGRAM_ENUM_MAX,  // TODO(ldemailly): enforce HistogramsNameMap match
 };
@@ -560,6 +562,7 @@ const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
     {BLOB_DB_GC_MICROS, "rocksdb.blobdb.gc.micros"},
     {BLOB_DB_COMPRESSION_MICROS, "rocksdb.blobdb.compression.micros"},
     {BLOB_DB_DECOMPRESSION_MICROS, "rocksdb.blobdb.decompression.micros"},
+    {FLUSH_TIME, "rocksdb.db.flush.micros"},
 };
 
 struct HistogramData {

java/rocksjni/portal.h

@@ -2806,8 +2806,10 @@ class HistogramTypeJni {
         return 0x1D;
       case rocksdb::Histograms::READ_NUM_MERGE_OPERANDS:
         return 0x1E;
-      case rocksdb::Histograms::HISTOGRAM_ENUM_MAX:
+      case rocksdb::Histograms::FLUSH_TIME:
         return 0x1F;
+      case rocksdb::Histograms::HISTOGRAM_ENUM_MAX:
+        return 0x20;
 
       default:
         // undefined/default
@@ -2882,6 +2884,8 @@ class HistogramTypeJni {
       case 0x1E:
         return rocksdb::Histograms::READ_NUM_MERGE_OPERANDS;
       case 0x1F:
+        return rocksdb::Histograms::FLUSH_TIME;
+      case 0x20:
         return rocksdb::Histograms::HISTOGRAM_ENUM_MAX;
 
       default: