Range deletion microoptimizations

Summary:
- Made RangeDelAggregator's InternalKeyComparator member a reference-to-const so we don't need to copy-construct it. Also added InternalKeyComparator to ImmutableCFOptions so we don't need to construct one for each DBIter.
- Made MemTable::NewRangeTombstoneIterator and the table readers' NewRangeTombstoneIterator() functions return nullptr instead of NewEmptyInternalIterator to avoid the allocation. Updated callers accordingly.
Closes https://github.com/facebook/rocksdb/pull/1548

Differential Revision: D4208169

Pulled By: ajkr

fbshipit-source-id: 2fd65cf

db/builder.cc

@@ -82,7 +82,6 @@ Status BuildTable(
   Status s;
   meta->fd.file_size = 0;
   iter->SeekToFirst();
-  range_del_iter->SeekToFirst();
   std::unique_ptr<RangeDelAggregator> range_del_agg(
       new RangeDelAggregator(internal_comparator, snapshots));
   s = range_del_agg->AddTombstones(std::move(range_del_iter));

db/db_compaction_filter_test.cc

@@ -261,8 +261,8 @@ TEST_F(DBTestCompactionFilter, CompactionFilter) {
   int total = 0;
   Arena arena;
   {
-    RangeDelAggregator range_del_agg(InternalKeyComparator(options.comparator),
-                                     {} /* snapshots */);
+    InternalKeyComparator icmp(options.comparator);
+    RangeDelAggregator range_del_agg(icmp, {} /* snapshots */);
     ScopedArenaIterator iter(
         dbfull()->NewInternalIterator(&arena, &range_del_agg, handles_[1]));
     iter->SeekToFirst();
@@ -351,8 +351,8 @@ TEST_F(DBTestCompactionFilter, CompactionFilter) {
   // level Lmax because this record is at the tip
   count = 0;
   {
-    RangeDelAggregator range_del_agg(InternalKeyComparator(options.comparator),
-                                     {} /* snapshots */);
+    InternalKeyComparator icmp(options.comparator);
+    RangeDelAggregator range_del_agg(icmp, {} /* snapshots */);
     ScopedArenaIterator iter(
         dbfull()->NewInternalIterator(&arena, &range_del_agg, handles_[1]));
     iter->SeekToFirst();
@@ -570,8 +570,8 @@ TEST_F(DBTestCompactionFilter, CompactionFilterContextManual) {
     int count = 0;
     int total = 0;
     Arena arena;
-    RangeDelAggregator range_del_agg(InternalKeyComparator(options.comparator),
-                                     {} /* snapshots */);
+    InternalKeyComparator icmp(options.comparator);
+    RangeDelAggregator range_del_agg(icmp, {} /* snapshots */);
     ScopedArenaIterator iter(
         dbfull()->NewInternalIterator(&arena, &range_del_agg));
     iter->SeekToFirst();

db/db_iter.cc

@@ -123,7 +123,7 @@ class DBIter: public Iterator {
         prefix_same_as_start_(prefix_same_as_start),
         pin_thru_lifetime_(pin_data),
         total_order_seek_(total_order_seek),
-        range_del_agg_(InternalKeyComparator(cmp), s) {
+        range_del_agg_(ioptions.internal_comparator, s) {
     RecordTick(statistics_, NO_ITERATORS);
     prefix_extractor_ = ioptions.prefix_extractor;
     max_skip_ = max_sequential_skip_in_iterations;

db/db_test_util.cc

@@ -590,8 +590,8 @@ std::string DBTestBase::Contents(int cf) {
 std::string DBTestBase::AllEntriesFor(const Slice& user_key, int cf) {
   Arena arena;
   auto options = CurrentOptions();
-  RangeDelAggregator range_del_agg(InternalKeyComparator(options.comparator),
-                                   {} /* snapshots */);
+  InternalKeyComparator icmp(options.comparator);
+  RangeDelAggregator range_del_agg(icmp, {} /* snapshots */);
   ScopedArenaIterator iter;
   if (cf == 0) {
     iter.set(dbfull()->NewInternalIterator(&arena, &range_del_agg));
@@ -999,8 +999,8 @@ void DBTestBase::validateNumberOfEntries(int numValues, int cf) {
   ScopedArenaIterator iter;
   Arena arena;
   auto options = CurrentOptions();
-  RangeDelAggregator range_del_agg(InternalKeyComparator(options.comparator),
-                                   {} /* snapshots */);
+  InternalKeyComparator icmp(options.comparator);
+  RangeDelAggregator range_del_agg(icmp, {} /* snapshots */);
   if (cf != 0) {
     iter.set(
         dbfull()->NewInternalIterator(&arena, &range_del_agg, handles_[cf]));

db/flush_job.cc

@@ -256,12 +256,14 @@ Status FlushJob::WriteLevel0Table() {
           "[%s] [JOB %d] Flushing memtable with next log file: %" PRIu64 "\n",
           cfd_->GetName().c_str(), job_context_->job_id, m->GetNextLogNumber());
       memtables.push_back(m->NewIterator(ro, &arena));
-      range_del_iters.push_back(m->NewRangeTombstoneIterator(ro));
+      auto* range_del_iter = m->NewRangeTombstoneIterator(ro);
+      if (range_del_iter != nullptr) {
+        range_del_iters.push_back(range_del_iter);
+      }
       total_num_entries += m->num_entries();
       total_num_deletes += m->num_deletes();
       total_memory_usage += m->ApproximateMemoryUsage();
     }
-    assert(memtables.size() == range_del_iters.size());
 
     event_logger_->Log() << "job" << job_context_->job_id << "event"
                          << "flush_started"

db/memtable.cc

@@ -75,6 +75,7 @@ MemTable::MemTable(const InternalKeyComparator& cmp,
       range_del_table_(SkipListFactory().CreateMemTableRep(
           comparator_, &allocator_, nullptr /* transform */,
           ioptions.info_log)),
+      is_range_del_table_empty_(true),
       data_size_(0),
       num_entries_(0),
       num_deletes_(0),
@@ -375,8 +376,8 @@ InternalIterator* MemTable::NewIterator(const ReadOptions& read_options,
 
 InternalIterator* MemTable::NewRangeTombstoneIterator(
     const ReadOptions& read_options) {
-  if (read_options.ignore_range_deletions) {
-    return NewEmptyInternalIterator();
+  if (read_options.ignore_range_deletions || is_range_del_table_empty_) {
+    return nullptr;
   }
   return new MemTableIterator(*this, read_options, nullptr /* arena */,
                               true /* use_range_del_table */);
@@ -508,6 +509,9 @@ void MemTable::Add(SequenceNumber s, ValueType type,
         !first_seqno_.compare_exchange_weak(cur_earliest_seqno, s)) {
     }
   }
+  if (is_range_del_table_empty_ && type == kTypeRangeDeletion) {
+    is_range_del_table_empty_ = false;
+  }
 }
 
 // Callback from MemTable::Get()

db/memtable.h

@@ -352,6 +352,7 @@ class MemTable {
   MemTableAllocator allocator_;
   unique_ptr<MemTableRep> table_;
   unique_ptr<MemTableRep> range_del_table_;
+  bool is_range_del_table_empty_;
 
   // Total data size of all data inserted
   std::atomic<uint64_t> data_size_;

db/range_del_aggregator.h

@@ -105,7 +105,7 @@ class RangeDelAggregator {
 
   SequenceNumber upper_bound_;
   std::unique_ptr<Rep> rep_;
-  const InternalKeyComparator icmp_;
+  const InternalKeyComparator& icmp_;
 };
 
 }  // namespace rocksdb

db/table_cache.cc

@@ -178,7 +178,9 @@ InternalIterator* TableCache::NewIterator(
   if (range_del_agg != nullptr && !options.ignore_range_deletions) {
     std::unique_ptr<InternalIterator> range_del_iter(NewRangeDeletionIterator(
         options, icomparator, fd, file_read_hist, skip_filters, level));
-    s = range_del_iter->status();
+    if (range_del_iter != nullptr) {
+      s = range_del_iter->status();
+    }
     if (s.ok()) {
       s = range_del_agg->AddTombstones(std::move(range_del_iter));
     }
@@ -253,7 +255,7 @@ InternalIterator* TableCache::NewRangeDeletionIterator(
     const FileDescriptor& fd, HistogramImpl* file_read_hist, bool skip_filters,
     int level) {
   if (options.ignore_range_deletions) {
-    return NewEmptyInternalIterator();
+    return nullptr;
   }
   Status s;
   TableReader* table_reader = fd.table_reader;
@@ -270,7 +272,11 @@ InternalIterator* TableCache::NewRangeDeletionIterator(
   if (s.ok()) {
     auto* result = table_reader->NewRangeTombstoneIterator(options);
     if (cache_handle != nullptr) {
-      result->RegisterCleanup(&UnrefEntry, cache_, cache_handle);
+      if (result == nullptr) {
+        ReleaseHandle(cache_handle);
+      } else {
+        result->RegisterCleanup(&UnrefEntry, cache_, cache_handle);
+      }
     }
     return result;
   }
@@ -287,7 +293,9 @@ Status TableCache::Get(const ReadOptions& options,
       !options.ignore_range_deletions) {
     std::unique_ptr<InternalIterator> range_del_iter(NewRangeDeletionIterator(
         options, internal_comparator, fd, file_read_hist, skip_filters, level));
-    s = range_del_iter->status();
+    if (range_del_iter != nullptr) {
+      s = range_del_iter->status();
+    }
     if (s.ok()) {
       s = get_context->range_del_agg()->AddTombstones(
           std::move(range_del_iter));

db/write_batch_test.cc

@@ -55,6 +55,9 @@ static std::string PrintContents(WriteBatch* b) {
       iter = mem->NewRangeTombstoneIterator(ReadOptions());
       iter_guard.reset(iter);
     }
+    if (iter == nullptr) {
+      continue;
+    }
     for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
       ParsedInternalKey ikey;
       memset((void*)&ikey, 0, sizeof(ikey));

table/block_based_table_reader.cc

@@ -1489,7 +1489,7 @@ InternalIterator* BlockBasedTable::NewIterator(const ReadOptions& read_options,
 InternalIterator* BlockBasedTable::NewRangeTombstoneIterator(
     const ReadOptions& read_options) {
   if (rep_->range_del_handle.IsNull()) {
-    return NewEmptyInternalIterator();
+    return nullptr;
   }
   std::string str;
   rep_->range_del_handle.EncodeTo(&str);
@@ -1967,18 +1967,20 @@ Status BlockBasedTable::DumpTable(WritableFile* out_file) {
   }
   // Output range deletions block
   auto* range_del_iter = NewRangeTombstoneIterator(ReadOptions());
-  range_del_iter->SeekToFirst();
-  if (range_del_iter->Valid()) {
-    out_file->Append(
-        "Range deletions:\n"
-        "--------------------------------------\n"
-        "  ");
-    for (; range_del_iter->Valid(); range_del_iter->Next()) {
-      DumpKeyValue(range_del_iter->key(), range_del_iter->value(), out_file);
+  if (range_del_iter != nullptr) {
+    range_del_iter->SeekToFirst();
+    if (range_del_iter->Valid()) {
+      out_file->Append(
+          "Range deletions:\n"
+          "--------------------------------------\n"
+          "  ");
+      for (; range_del_iter->Valid(); range_del_iter->Next()) {
+        DumpKeyValue(range_del_iter->key(), range_del_iter->value(), out_file);
+      }
+      out_file->Append("\n");
     }
-    out_file->Append("\n");
+    delete range_del_iter;
   }
-  delete range_del_iter;
   // Output Data blocks
   s = DumpDataBlocks(out_file);
 

table/table_reader.h

@@ -44,7 +44,7 @@ class TableReader {
 
   virtual InternalIterator* NewRangeTombstoneIterator(
       const ReadOptions& read_options) {
-    return NewEmptyInternalIterator();
+    return nullptr;
   }
 
   // Given a key, return an approximate byte offset in the file where

table/table_test.cc

@@ -2459,6 +2459,9 @@ TEST_F(MemTableTest, Simple) {
       iter = memtable->NewRangeTombstoneIterator(ReadOptions());
       iter_guard.reset(iter);
     }
+    if (iter == nullptr) {
+      continue;
+    }
     iter->SeekToFirst();
     while (iter->Valid()) {
       fprintf(stderr, "key: '%s' -> '%s'\n", iter->key().ToString().c_str(),

tools/ldb_cmd.cc

@@ -1187,8 +1187,8 @@ void InternalDumpCommand::DoCommand() {
   uint64_t s1=0,s2=0;
   // Setup internal key iterator
   Arena arena;
-  RangeDelAggregator range_del_agg(InternalKeyComparator(options_.comparator),
-                                   {} /* snapshots */);
+  auto icmp = InternalKeyComparator(options_.comparator);
+  RangeDelAggregator range_del_agg(icmp, {} /* snapshots */);
   ScopedArenaIterator iter(idb->NewInternalIterator(&arena, &range_del_agg));
   Status st = iter->status();
   if (!st.ok()) {

util/cf_options.cc

@@ -31,6 +31,7 @@ ImmutableCFOptions::ImmutableCFOptions(const ImmutableDBOptions& db_options,
       compaction_options_fifo(cf_options.compaction_options_fifo),
       prefix_extractor(cf_options.prefix_extractor.get()),
       user_comparator(cf_options.comparator),
+      internal_comparator(InternalKeyComparator(cf_options.comparator)),
       merge_operator(cf_options.merge_operator.get()),
       compaction_filter(cf_options.compaction_filter),
       compaction_filter_factory(cf_options.compaction_filter_factory.get()),

util/cf_options.h

@@ -8,6 +8,7 @@
 #include <string>
 #include <vector>
 
+#include "db/dbformat.h"
 #include "rocksdb/options.h"
 #include "util/compression.h"
 #include "util/db_options.h"
@@ -35,6 +36,7 @@ struct ImmutableCFOptions {
   const SliceTransform* prefix_extractor;
 
   const Comparator* user_comparator;
+  InternalKeyComparator internal_comparator;
 
   MergeOperator* merge_operator;