Add statistic histogram "rocksdb.sst.read.micros"

Summary: Measure read latency histogram and put in statistics. Compaction inputs are excluded from it when possible (unfortunately usually no possible as we usually take table reader from table cache.

Test Plan:
Run db_bench and it shows the stats, like:

rocksdb.sst.read.micros statistics Percentiles :=> 50 : 1.238522 95 : 2.529740 99 : 3.912180

Reviewers: kradhakrishnan, rven, anthony, IslamAbdelRahman, MarkCallaghan, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D43275

db/compaction_job.cc

@@ -716,7 +716,8 @@ Status CompactionJob::FinishCompactionOutputFile(const Status& input_status) {
     ColumnFamilyData* cfd = compact_->compaction->column_family_data();
     FileDescriptor fd(output_number, output_path_id, current_bytes);
     Iterator* iter = cfd->table_cache()->NewIterator(
-        ReadOptions(), env_options_, cfd->internal_comparator(), fd);
+        ReadOptions(), env_options_, cfd->internal_comparator(), fd, nullptr,
+        true);
     s = iter->status();
 
     if (s.ok() && paranoid_file_checks_) {

db/table_cache.cc

@@ -79,7 +79,7 @@ void TableCache::ReleaseHandle(Cache::Handle* handle) {
 Status TableCache::FindTable(const EnvOptions& env_options,
                              const InternalKeyComparator& internal_comparator,
                              const FileDescriptor& fd, Cache::Handle** handle,
-                             const bool no_io) {
+                             const bool no_io, bool record_read_stats) {
   PERF_TIMER_GUARD(find_table_nanos);
   Status s;
   uint64_t number = fd.GetNumber();
@@ -101,7 +101,10 @@ Status TableCache::FindTable(const EnvOptions& env_options,
       }
       StopWatch sw(ioptions_.env, ioptions_.statistics, TABLE_OPEN_IO_MICROS);
       std::unique_ptr<RandomAccessFileReader> file_reader(
-          new RandomAccessFileReader(std::move(file)));
+          new RandomAccessFileReader(
+              std::move(file), ioptions_.env,
+              record_read_stats ? ioptions_.statistics : nullptr,
+              SST_READ_MICROS));
       s = ioptions_.table_factory->NewTableReader(
           ioptions_, env_options, internal_comparator, std::move(file_reader),
           fd.GetFileSize(), &table_reader);
@@ -136,7 +139,7 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
   Status s;
   if (table_reader == nullptr) {
     s = FindTable(env_options, icomparator, fd, &handle,
-                  options.read_tier == kBlockCacheTier);
+                  options.read_tier == kBlockCacheTier, !for_compaction);
     if (!s.ok()) {
       return NewErrorIterator(s, arena);
     }

db/table_cache.h

@@ -63,7 +63,7 @@ class TableCache {
   Status FindTable(const EnvOptions& toptions,
                    const InternalKeyComparator& internal_comparator,
                    const FileDescriptor& file_fd, Cache::Handle**,
-                   const bool no_io = false);
+                   const bool no_io = false, bool record_read_stats = true);
 
   // Get TableReader from a cache handle.
   TableReader* GetTableReaderFromHandle(Cache::Handle* handle);

include/rocksdb/statistics.h

@@ -251,6 +251,7 @@ enum Histograms : uint32_t {
   NUM_FILES_IN_SINGLE_COMPACTION,
   DB_SEEK,
   WRITE_STALL,
+  SST_READ_MICROS,
   HISTOGRAM_ENUM_MAX,  // TODO(ldemailly): enforce HistogramsNameMap match
 };
 
@@ -275,6 +276,7 @@ const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
     {NUM_FILES_IN_SINGLE_COMPACTION, "rocksdb.numfiles.in.singlecompaction"},
     {DB_SEEK, "rocksdb.db.seek.micros"},
     {WRITE_STALL, "rocksdb.db.write.stall"},
+    {SST_READ_MICROS, "rocksdb.sst.read.micros"},
 };
 
 struct HistogramData {

util/file_reader_writer.cc

@@ -27,6 +27,7 @@ Status SequentialFileReader::Skip(uint64_t n) { return file_->Skip(n); }
 
 Status RandomAccessFileReader::Read(uint64_t offset, size_t n, Slice* result,
                                     char* scratch) const {
+  StopWatch sw(env_, stats_, hist_type_);
   IOSTATS_TIMER_GUARD(read_nanos);
   Status s = file_->Read(offset, n, result, scratch);
   IOSTATS_ADD_IF_POSITIVE(bytes_read, result->size());

util/file_reader_writer.h

@@ -10,6 +10,9 @@
 #include "rocksdb/env.h"
 
 namespace rocksdb {
+
+class Statistics;
+
 class SequentialFileReader {
  private:
   std::unique_ptr<SequentialFile> file_;
@@ -27,10 +30,19 @@ class SequentialFileReader {
 class RandomAccessFileReader : public RandomAccessFile {
  private:
   std::unique_ptr<RandomAccessFile> file_;
+  Env* env_;
+  Statistics* stats_;
+  uint32_t hist_type_;
 
  public:
-  explicit RandomAccessFileReader(std::unique_ptr<RandomAccessFile>&& raf)
-      : file_(std::move(raf)) {}
+  explicit RandomAccessFileReader(std::unique_ptr<RandomAccessFile>&& raf,
+                                  Env* env = nullptr,
+                                  Statistics* stats = nullptr,
+                                  uint32_t hist_type = 0)
+      : file_(std::move(raf)),
+        env_(env),
+        stats_(stats),
+        hist_type_(hist_type) {}
 
   Status Read(uint64_t offset, size_t n, Slice* result, char* scratch) const;