Measure file read latency histogram per level

Summary: In internal stats, remember read latency histogram, if statistics is enabled. It can be retrieved from DB::GetProperty() with "rocksdb.dbstats" property, if it is enabled.

Test Plan: Manually run db_bench and prints out "rocksdb.dbstats" by hand and make sure it prints out as expected

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

Reviewed By: yhchiang

Subscribers: MarkCallaghan, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D44193

db/builder.cc

@@ -12,6 +12,7 @@
 #include <vector>
 #include "db/dbformat.h"
 #include "db/filename.h"
+#include "db/internal_stats.h"
 #include "db/merge_helper.h"
 #include "db/table_cache.h"
 #include "db/version_edit.h"
@@ -54,7 +55,8 @@ Status BuildTable(
     const SequenceNumber earliest_seqno_in_memtable,
     const CompressionType compression,
     const CompressionOptions& compression_opts, bool paranoid_file_checks,
-    const Env::IOPriority io_priority, TableProperties* table_properties) {
+    InternalStats* internal_stats, const Env::IOPriority io_priority,
+    TableProperties* table_properties) {
   // Reports the IOStats for flush for every following bytes.
   const size_t kReportFlushIOStatsEvery = 1048576;
   Status s;
@@ -248,8 +250,11 @@ Status BuildTable(
 
     if (s.ok()) {
       // Verify that the table is usable
-      Iterator* it = table_cache->NewIterator(ReadOptions(), env_options,
+      Iterator* it = table_cache->NewIterator(
-                                              internal_comparator, meta->fd);
+          ReadOptions(), env_options, internal_comparator, meta->fd, nullptr,
+          (internal_stats == nullptr) ? nullptr
+                                      : internal_stats->GetFileReadHist(0),
+          false);
       s = it->status();
       if (s.ok() && paranoid_file_checks) {
         for (it->SeekToFirst(); it->Valid(); it->Next()) {}

db/builder.h

@@ -30,6 +30,7 @@ class TableCache;
 class VersionEdit;
 class TableBuilder;
 class WritableFileWriter;
+class InternalStats;
 
 TableBuilder* NewTableBuilder(
     const ImmutableCFOptions& options,
@@ -55,6 +56,7 @@ extern Status BuildTable(
     const SequenceNumber earliest_seqno_in_memtable,
     const CompressionType compression,
     const CompressionOptions& compression_opts, bool paranoid_file_checks,
+    InternalStats* internal_stats,
     const Env::IOPriority io_priority = Env::IO_HIGH,
     TableProperties* table_properties = nullptr);
 

db/compaction_job.cc

@@ -760,7 +760,9 @@ Status CompactionJob::FinishCompactionOutputFile(const Status& input_status) {
     FileDescriptor fd(output_number, output_path_id, current_bytes);
     Iterator* iter = cfd->table_cache()->NewIterator(
         ReadOptions(), env_options_, cfd->internal_comparator(), fd, nullptr,
-        true);
+        cfd->internal_stats()->GetFileReadHist(
+            compact_->compaction->output_level()),
+        false);
     s = iter->status();
 
     if (s.ok() && paranoid_file_checks_) {

db/db_impl.cc

@@ -1293,8 +1293,8 @@ Status DBImpl::WriteLevel0TableForRecovery(int job_id, ColumnFamilyData* cfd,
           iter.get(), &meta, cfd->internal_comparator(),
           cfd->int_tbl_prop_collector_factories(), newest_snapshot,
           earliest_seqno_in_memtable, GetCompressionFlush(*cfd->ioptions()),
-          cfd->ioptions()->compression_opts, paranoid_file_checks, Env::IO_HIGH,
+          cfd->ioptions()->compression_opts, paranoid_file_checks,
-          &info.table_properties);
+          cfd->internal_stats(), Env::IO_HIGH, &info.table_properties);
       LogFlush(db_options_.info_log);
       Log(InfoLogLevel::DEBUG_LEVEL, db_options_.info_log,
           "[%s] [WriteLevel0TableForRecovery]"

db/flush_job.cc

@@ -232,14 +232,14 @@ Status FlushJob::WriteLevel0Table(const autovector<MemTable*>& mems,
 
       TEST_SYNC_POINT_CALLBACK("FlushJob::WriteLevel0Table:output_compression",
                                &output_compression_);
-      s = BuildTable(dbname_, db_options_.env, *cfd_->ioptions(), env_options_,
+      s = BuildTable(
-                     cfd_->table_cache(), iter.get(), meta,
+          dbname_, db_options_.env, *cfd_->ioptions(), env_options_,
-                     cfd_->internal_comparator(),
+          cfd_->table_cache(), iter.get(), meta, cfd_->internal_comparator(),
           cfd_->int_tbl_prop_collector_factories(), newest_snapshot_,
           earliest_seqno_in_memtable, output_compression_,
           cfd_->ioptions()->compression_opts,
-                     mutable_cf_options_.paranoid_file_checks, Env::IO_HIGH,
+          mutable_cf_options_.paranoid_file_checks, cfd_->internal_stats(),
-                     &info.table_properties);
+          Env::IO_HIGH, &info.table_properties);
       LogFlush(db_options_.info_log);
     }
     Log(InfoLogLevel::INFO_LEVEL, db_options_.info_log,

db/forward_iterator.cc

@@ -47,7 +47,8 @@ class LevelIterator : public Iterator {
     assert(file_index_ < files_.size());
     file_iter_.reset(cfd_->table_cache()->NewIterator(
         read_options_, *(cfd_->soptions()), cfd_->internal_comparator(),
-        files_[file_index_]->fd, nullptr /* table_reader_ptr */, false));
+        files_[file_index_]->fd, nullptr /* table_reader_ptr */, nullptr,
+        false));
   }
   void SeekToLast() override {
     status_ = Status::NotSupported("LevelIterator::SeekToLast()");

db/internal_stats.cc

@@ -540,6 +540,16 @@ void InternalStats::DumpDBStats(std::string* value) {
                10000.0 / std::max(interval_seconds_up, 0.001));
   value->append(buf);
 
+  for (int level = 0; level < number_levels_; level++) {
+    if (!file_read_latency_[level].Empty()) {
+      char buf2[5000];
+      snprintf(buf2, sizeof(buf2),
+               "** Level %d read latency histogram (micros):\n%s\n", level,
+               file_read_latency_[level].ToString().c_str());
+      value->append(buf2);
+    }
+  }
+
   db_stats_snapshot_.seconds_up = seconds_up;
   db_stats_snapshot_.ingest_bytes = user_bytes_written;
   db_stats_snapshot_.write_other = write_other;

db/internal_stats.h

@@ -98,6 +98,7 @@ class InternalStats {
         comp_stats_(num_levels),
         stall_leveln_slowdown_count_hard_(num_levels),
         stall_leveln_slowdown_count_soft_(num_levels),
+        file_read_latency_(num_levels),
         bg_error_count_(0),
         number_levels_(num_levels),
         env_(env),
@@ -238,6 +239,10 @@ class InternalStats {
     db_stats_[type] += value;
   }
 
+  HistogramImpl* GetFileReadHist(int level) {
+    return &file_read_latency_[level];
+  }
+
   uint64_t GetBackgroundErrorCount() const { return bg_error_count_; }
 
   uint64_t BumpAndGetBackgroundErrorCount() { return ++bg_error_count_; }
@@ -265,6 +270,7 @@ class InternalStats {
   // These count the number of microseconds for which MakeRoomForWrite stalls.
   std::vector<uint64_t> stall_leveln_slowdown_count_hard_;
   std::vector<uint64_t> stall_leveln_slowdown_count_soft_;
+  std::vector<HistogramImpl> file_read_latency_;
 
   // Used to compute per-interval statistics
   struct CFStatsSnapshot {
@@ -389,6 +395,8 @@ class InternalStats {
 
   void AddDBStats(InternalDBStatsType type, uint64_t value) {}
 
+  HistogramImpl* GetFileReadHist(int level) { return nullptr; }
+
   uint64_t GetBackgroundErrorCount() const { return 0; }
 
   uint64_t BumpAndGetBackgroundErrorCount() { return 0; }

db/repair.cc

@@ -293,7 +293,7 @@ class Repairer {
       status = BuildTable(dbname_, env_, ioptions_, env_options_, table_cache_,
                           iter.get(), &meta, icmp_,
                           &int_tbl_prop_collector_factories_, 0, 0,
-                          kNoCompression, CompressionOptions(), false);
+                          kNoCompression, CompressionOptions(), false, nullptr);
     }
     delete mem->Unref();
     delete cf_mems_default;

db/table_cache.cc

@@ -79,7 +79,8 @@ 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, bool record_read_stats) {
+                             const bool no_io, bool record_read_stats,
+                             HistogramImpl* file_read_hist) {
   PERF_TIMER_GUARD(find_table_nanos);
   Status s;
   uint64_t number = fd.GetNumber();
@@ -104,7 +105,7 @@ Status TableCache::FindTable(const EnvOptions& env_options,
           new RandomAccessFileReader(
               std::move(file), ioptions_.env,
               record_read_stats ? ioptions_.statistics : nullptr,
-              SST_READ_MICROS));
+              SST_READ_MICROS, file_read_hist));
       s = ioptions_.table_factory->NewTableReader(
           ioptions_, env_options, internal_comparator, std::move(file_reader),
           fd.GetFileSize(), &table_reader);
@@ -128,6 +129,7 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
                                   const InternalKeyComparator& icomparator,
                                   const FileDescriptor& fd,
                                   TableReader** table_reader_ptr,
+                                  HistogramImpl* file_read_hist,
                                   bool for_compaction, Arena* arena) {
   PERF_TIMER_GUARD(new_table_iterator_nanos);
 
@@ -139,7 +141,8 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
   Status s;
   if (table_reader == nullptr) {
     s = FindTable(env_options, icomparator, fd, &handle,
-                  options.read_tier == kBlockCacheTier, !for_compaction);
+                  options.read_tier == kBlockCacheTier, !for_compaction,
+                  file_read_hist);
     if (!s.ok()) {
       return NewErrorIterator(s, arena);
     }
@@ -164,7 +167,7 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
 Status TableCache::Get(const ReadOptions& options,
                        const InternalKeyComparator& internal_comparator,
                        const FileDescriptor& fd, const Slice& k,
-                       GetContext* get_context) {
+                       GetContext* get_context, HistogramImpl* file_read_hist) {
   TableReader* t = fd.table_reader;
   Status s;
   Cache::Handle* handle = nullptr;
@@ -210,7 +213,7 @@ Status TableCache::Get(const ReadOptions& options,
 
   if (!t) {
     s = FindTable(env_options_, internal_comparator, fd, &handle,
-                  options.read_tier == kBlockCacheTier);
+                  options.read_tier == kBlockCacheTier, file_read_hist);
     if (s.ok()) {
       t = GetTableReaderFromHandle(handle);
     }

db/table_cache.h

@@ -28,6 +28,7 @@ class Env;
 class Arena;
 struct FileDescriptor;
 class GetContext;
+class HistogramImpl;
 
 class TableCache {
  public:
@@ -46,6 +47,7 @@ class TableCache {
                         const InternalKeyComparator& internal_comparator,
                         const FileDescriptor& file_fd,
                         TableReader** table_reader_ptr = nullptr,
+                        HistogramImpl* file_read_hist = nullptr,
                         bool for_compaction = false, Arena* arena = nullptr);
 
   // If a seek to internal key "k" in specified file finds an entry,
@@ -54,7 +56,7 @@ class TableCache {
   Status Get(const ReadOptions& options,
              const InternalKeyComparator& internal_comparator,
              const FileDescriptor& file_fd, const Slice& k,
-             GetContext* get_context);
+             GetContext* get_context, HistogramImpl* file_read_hist = nullptr);
 
   // Evict any entry for the specified file number
   static void Evict(Cache* cache, uint64_t file_number);
@@ -63,7 +65,8 @@ class TableCache {
   Status FindTable(const EnvOptions& toptions,
                    const InternalKeyComparator& internal_comparator,
                    const FileDescriptor& file_fd, Cache::Handle**,
-                   const bool no_io = false, bool record_read_stats = true);
+                   const bool no_io = false, bool record_read_stats = true,
+                   HistogramImpl* file_read_hist = nullptr);
 
   // Get TableReader from a cache handle.
   TableReader* GetTableReaderFromHandle(Cache::Handle* handle);

db/version_set.cc

@@ -24,6 +24,7 @@
 #include <string>
 
 #include "db/filename.h"
+#include "db/internal_stats.h"
 #include "db/log_reader.h"
 #include "db/log_writer.h"
 #include "db/memtable.h"
@@ -474,12 +475,17 @@ class LevelFileNumIterator : public Iterator {
 class LevelFileIteratorState : public TwoLevelIteratorState {
  public:
   LevelFileIteratorState(TableCache* table_cache,
-    const ReadOptions& read_options, const EnvOptions& env_options,
+                         const ReadOptions& read_options,
-    const InternalKeyComparator& icomparator, bool for_compaction,
+                         const EnvOptions& env_options,
+                         const InternalKeyComparator& icomparator,
+                         HistogramImpl* file_read_hist, bool for_compaction,
                          bool prefix_enabled)
       : TwoLevelIteratorState(prefix_enabled),
-      table_cache_(table_cache), read_options_(read_options),
+        table_cache_(table_cache),
-      env_options_(env_options), icomparator_(icomparator),
+        read_options_(read_options),
+        env_options_(env_options),
+        icomparator_(icomparator),
+        file_read_hist_(file_read_hist),
         for_compaction_(for_compaction) {}
 
   Iterator* NewSecondaryIterator(const Slice& meta_handle) override {
@@ -491,7 +497,8 @@ class LevelFileIteratorState : public TwoLevelIteratorState {
           reinterpret_cast<const FileDescriptor*>(meta_handle.data());
       return table_cache_->NewIterator(
           read_options_, env_options_, icomparator_, *fd,
-          nullptr /* don't need reference to table*/, for_compaction_);
+          nullptr /* don't need reference to table*/, file_read_hist_,
+          for_compaction_);
     }
   }
 
@@ -504,6 +511,7 @@ class LevelFileIteratorState : public TwoLevelIteratorState {
   const ReadOptions read_options_;
   const EnvOptions& env_options_;
   const InternalKeyComparator& icomparator_;
+  HistogramImpl* file_read_hist_;
   bool for_compaction_;
 };
 
@@ -705,7 +713,7 @@ void Version::AddIterators(const ReadOptions& read_options,
     const auto& file = storage_info_.LevelFilesBrief(0).files[i];
     merge_iter_builder->AddIterator(cfd_->table_cache()->NewIterator(
         read_options, soptions, cfd_->internal_comparator(), file.fd, nullptr,
-        false, arena));
+        cfd_->internal_stats()->GetFileReadHist(0), false, arena));
   }
 
   // For levels > 0, we can use a concatenating iterator that sequentially
@@ -714,9 +722,11 @@ void Version::AddIterators(const ReadOptions& read_options,
   for (int level = 1; level < storage_info_.num_non_empty_levels(); level++) {
     if (storage_info_.LevelFilesBrief(level).num_files != 0) {
       auto* mem = arena->AllocateAligned(sizeof(LevelFileIteratorState));
-      auto* state = new (mem) LevelFileIteratorState(
+      auto* state = new (mem)
-          cfd_->table_cache(), read_options, soptions,
+          LevelFileIteratorState(cfd_->table_cache(), read_options, soptions,
-          cfd_->internal_comparator(), false /* for_compaction */,
+                                 cfd_->internal_comparator(),
+                                 cfd_->internal_stats()->GetFileReadHist(level),
+                                 false /* for_compaction */,
                                  cfd_->ioptions()->prefix_extractor != nullptr);
       mem = arena->AllocateAligned(sizeof(LevelFileNumIterator));
       auto* first_level_iter = new (mem) LevelFileNumIterator(
@@ -810,8 +820,9 @@ void Version::Get(const ReadOptions& read_options,
       user_comparator(), internal_comparator());
   FdWithKeyRange* f = fp.GetNextFile();
   while (f != nullptr) {
-    *status = table_cache_->Get(read_options, *internal_comparator(), f->fd,
+    *status = table_cache_->Get(
-                                ikey, &get_context);
+        read_options, *internal_comparator(), f->fd, ikey, &get_context,
+        cfd_->internal_stats()->GetFileReadHist(fp.GetHitFileLevel()));
     // TODO: examine the behavior for corrupted key
     if (!status->ok()) {
       return;
@@ -3059,14 +3070,17 @@ Iterator* VersionSet::MakeInputIterator(Compaction* c) {
           list[num++] = cfd->table_cache()->NewIterator(
               read_options, env_options_compactions_,
               cfd->internal_comparator(), flevel->files[i].fd, nullptr,
+              nullptr, /* no per level latency histogram*/
               true /* for compaction */);
         }
       } else {
         // Create concatenating iterator for the files from this level
-        list[num++] = NewTwoLevelIterator(new LevelFileIteratorState(
+        list[num++] = NewTwoLevelIterator(
+            new LevelFileIteratorState(
                 cfd->table_cache(), read_options, env_options_,
-              cfd->internal_comparator(), true /* for_compaction */,
+                cfd->internal_comparator(),
-              false /* prefix enabled */),
+                nullptr /* no per level latency histogram */,
+                true /* for_compaction */, false /* prefix enabled */),
             new LevelFileNumIterator(cfd->internal_comparator(),
                                      c->input_levels(which)));
       }

util/file_reader_writer.cc

@@ -11,6 +11,7 @@
 
 #include <algorithm>
 #include "port/port.h"
+#include "util/histogram.h"
 #include "util/iostats_context_imp.h"
 #include "util/random.h"
 #include "util/rate_limiter.h"
@@ -27,10 +28,18 @@ 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_);
+  Status s;
+  uint64_t elapsed = 0;
+  {
+    StopWatch sw(env_, stats_, hist_type_,
+                 (stats_ != nullptr) ? &elapsed : nullptr);
     IOSTATS_TIMER_GUARD(read_nanos);
-  Status s = file_->Read(offset, n, result, scratch);
+    s = file_->Read(offset, n, result, scratch);
     IOSTATS_ADD_IF_POSITIVE(bytes_read, result->size());
+  }
+  if (stats_ != nullptr && file_read_hist_ != nullptr) {
+    file_read_hist_->Add(elapsed);
+  }
   return s;
 }
 

util/file_reader_writer.h

@@ -12,6 +12,7 @@
 namespace rocksdb {
 
 class Statistics;
+class HistogramImpl;
 
 class SequentialFileReader {
  private:
@@ -33,16 +34,19 @@ class RandomAccessFileReader : public RandomAccessFile {
   Env* env_;
   Statistics* stats_;
   uint32_t hist_type_;
+  HistogramImpl* file_read_hist_;
 
  public:
   explicit RandomAccessFileReader(std::unique_ptr<RandomAccessFile>&& raf,
                                   Env* env = nullptr,
                                   Statistics* stats = nullptr,
-                                  uint32_t hist_type = 0)
+                                  uint32_t hist_type = 0,
+                                  HistogramImpl* file_read_hist = nullptr)
       : file_(std::move(raf)),
         env_(env),
         stats_(stats),
-        hist_type_(hist_type) {}
+        hist_type_(hist_type),
+        file_read_hist_(file_read_hist) {}
 
   Status Read(uint64_t offset, size_t n, Slice* result, char* scratch) const;