Moving sequence number compaction variables from SubCompactionState to CompactionJob

Summary:
It was pointed out to me that the members of SubCompactionState
'earliest_snapshot', 'latest_snapshot' and 'visible_at_tip' are never
modified by the subcompactions, so they can stay as global varaibles
instead to make things simpler.

Test Plan: make all && make check

Reviewers: sdong, igor, noetzli, anthony, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D45477

HISTORY.md

@@ -7,7 +7,7 @@
 
 ### Public API Changes
 * Removed class Env::RandomRWFile and Env::NewRandomRWFile().
-* Renamed DBOptions.num_subcompactions to DBOptions.max_subcompactions to make the name better match the actual funcionality of the option.
+* Renamed DBOptions.num_subcompactions to DBOptions.max_subcompactions to make the name better match the actual functionality of the option.
 
 ## 3.13.0 (8/6/2015)
 ### New Features

db/compaction_job.cc

@@ -100,9 +100,6 @@ struct CompactionJob::SubCompactionState {
   uint64_t total_bytes;
   uint64_t num_input_records;
   uint64_t num_output_records;
-  SequenceNumber earliest_snapshot;
-  SequenceNumber visible_at_tip;
-  SequenceNumber latest_snapshot;
   CompactionJobStats compaction_job_stats;
 
   // "level_ptrs" holds indices that remember which file of an associated
@@ -113,20 +110,15 @@ struct CompactionJob::SubCompactionState {
   // is in or beyond the last file checked during the previous call
   std::vector<size_t> level_ptrs;
 
-  SubCompactionState(Compaction* c, Slice* _start, Slice* _end,
-                     SequenceNumber earliest, SequenceNumber visible,
-                     SequenceNumber latest)
-    : compaction(c),
-      start(_start),
-      end(_end),
-      outfile(nullptr),
-      builder(nullptr),
-      total_bytes(0),
-      num_input_records(0),
-      num_output_records(0),
-      earliest_snapshot(earliest),
-      visible_at_tip(visible),
-      latest_snapshot(latest) {
+  SubCompactionState(Compaction* c, Slice* _start, Slice* _end)
+      : compaction(c),
+        start(_start),
+        end(_end),
+        outfile(nullptr),
+        builder(nullptr),
+        total_bytes(0),
+        num_input_records(0),
+        num_output_records(0) {
     assert(compaction != nullptr);
     level_ptrs = std::vector<size_t>(compaction->number_levels(), 0);
   }
@@ -146,9 +138,6 @@ struct CompactionJob::SubCompactionState {
     total_bytes = std::move(o.total_bytes);
     num_input_records = std::move(o.num_input_records);
     num_output_records = std::move(o.num_output_records);
-    earliest_snapshot = std::move(o.earliest_snapshot);
-    visible_at_tip = std::move(o.visible_at_tip);
-    latest_snapshot = std::move(o.latest_snapshot);
     level_ptrs = std::move(o.level_ptrs);
     return *this;
   }
@@ -321,32 +310,29 @@ void CompactionJob::Prepare() {
   bottommost_level_ = c->bottommost_level();
 
   // Initialize subcompaction states
-  SequenceNumber earliest_snapshot;
-  SequenceNumber latest_snapshot = 0;
-  SequenceNumber visible_at_tip = 0;
+  latest_snapshot_ = 0;
+  visible_at_tip_ = 0;
 
   if (existing_snapshots_.size() == 0) {
     // optimize for fast path if there are no snapshots
-    visible_at_tip = versions_->LastSequence();
-    earliest_snapshot = visible_at_tip;
+    visible_at_tip_ = versions_->LastSequence();
+    earliest_snapshot_ = visible_at_tip_;
   } else {
-    latest_snapshot = existing_snapshots_.back();
+    latest_snapshot_ = existing_snapshots_.back();
     // Add the current seqno as the 'latest' virtual
     // snapshot to the end of this list.
     existing_snapshots_.push_back(versions_->LastSequence());
-    earliest_snapshot = existing_snapshots_[0];
+    earliest_snapshot_ = existing_snapshots_[0];
   }
 
-  InitializeSubCompactions(earliest_snapshot, visible_at_tip, latest_snapshot);
+  InitializeSubCompactions();
 }
 
 // For L0-L1 compaction, iterators work in parallel by processing
 // different subsets of the full key range. This function sets up
 // the local states used by each of these subcompactions during
 // their execution
-void CompactionJob::InitializeSubCompactions(const SequenceNumber& earliest,
-                                             const SequenceNumber& visible,
-                                             const SequenceNumber& latest) {
+void CompactionJob::InitializeSubCompactions() {
   Compaction* c = compact_->compaction;
   auto& bounds = sub_compaction_boundaries_;
   if (c->IsSubCompaction()) {
@@ -410,8 +396,7 @@ void CompactionJob::InitializeSubCompactions(const SequenceNumber& earliest,
   for (size_t i = 0; i <= bounds.size(); i++) {
     Slice *start = i == 0 ? nullptr : &bounds[i - 1];
     Slice *end = i == bounds.size() ? nullptr : &bounds[i];
-    compact_->sub_compact_states.emplace_back(compact_->compaction, start,
-        end, earliest, visible, latest);
+    compact_->sub_compact_states.emplace_back(compact_->compaction, start, end);
   }
 }
 
@@ -658,8 +643,7 @@ void CompactionJob::ProcessKeyValueCompaction(SubCompactionState* sub_compact) {
       visible_in_snapshot = kMaxSequenceNumber;
       // apply the compaction filter to the first occurrence of the user key
       if (compaction_filter && ikey.type == kTypeValue &&
-          (sub_compact->visible_at_tip ||
-            ikey.sequence > sub_compact->latest_snapshot)) {
+          (visible_at_tip_ || ikey.sequence > latest_snapshot_)) {
         // If the user has specified a compaction filter and the sequence
         // number is greater than any external snapshot, then invoke the
         // filter. If the return value of the compaction filter is true,
@@ -695,9 +679,8 @@ void CompactionJob::ProcessKeyValueCompaction(SubCompactionState* sub_compact) {
     // the earlist snapshot that is affected by this kv.
     SequenceNumber prev_snapshot = 0;  // 0 means no previous snapshot
     SequenceNumber visible =
-        sub_compact->visible_at_tip
-            ? sub_compact->visible_at_tip
-            : findEarliestVisibleSnapshot(ikey.sequence, &prev_snapshot);
+        visible_at_tip_ ? visible_at_tip_ : findEarliestVisibleSnapshot(
+                                                ikey.sequence, &prev_snapshot);
 
     if (visible_in_snapshot == visible) {
       // If the earliest snapshot is which this key is visible in
@@ -709,7 +692,7 @@ void CompactionJob::ProcessKeyValueCompaction(SubCompactionState* sub_compact) {
       ++key_drop_newer_entry;
       input->Next();  // (A)
     } else if (ikey.type == kTypeDeletion &&
-               ikey.sequence <= sub_compact->earliest_snapshot &&
+               ikey.sequence <= earliest_snapshot_ &&
                sub_compact->compaction->KeyNotExistsBeyondOutputLevel(
                    ikey.user_key, &sub_compact->level_ptrs)) {
       // For this user key:
@@ -815,7 +798,7 @@ Status CompactionJob::WriteKeyValue(const Slice& key, const Slice& value,
   // If this is the bottommost level (no files in lower levels)
   // and the earliest snapshot is larger than this seqno
   // then we can squash the seqno to zero.
-  if (bottommost_level_ && ikey.sequence < sub_compact->earliest_snapshot &&
+  if (bottommost_level_ && ikey.sequence < earliest_snapshot_ &&
       ikey.type != kTypeMerge) {
     assert(ikey.type != kTypeDeletion);
     // make a copy because updating in place would cause problems

db/compaction_job.h

@@ -83,9 +83,7 @@ class CompactionJob {
 
   void AggregateStatistics();
   // Set up the individual states used by each subcompaction
-  void InitializeSubCompactions(const SequenceNumber& earliest,
-                                const SequenceNumber& visible,
-                                const SequenceNumber& latest);
+  void InitializeSubCompactions();
 
   // update the thread status for starting a compaction.
   void ReportStartedCompaction(Compaction* compaction);
@@ -132,6 +130,10 @@ class CompactionJob {
 
   InternalStats::CompactionStats compaction_stats_;
 
+  SequenceNumber earliest_snapshot_;
+  SequenceNumber latest_snapshot_;
+  SequenceNumber visible_at_tip_;
+
   // DBImpl state
   const std::string& dbname_;
   const DBOptions& db_options_;