Basic MultiGet support for partitioned filters (#6757)

Summary:
In MultiGet, access each applicable filter partition only once
per batch, rather than for each applicable key. Also,

* Fix Bloom stats for MultiGet
* Fix/refactor MultiGetContext::Range::KeysLeft, including
* Add efficient BitsSetToOne implementation
* Assert that MultiGetContext::Range does not go beyond shift range

Performance test: Generate db:

    $ ./db_bench --benchmarks=fillrandom --num=15000000 --cache_index_and_filter_blocks -bloom_bits=10 -partition_index_and_filters=true
    ...

Before (middle performing run of three; note some missing Bloom stats):

    $ ./db_bench --use-existing-db --benchmarks=multireadrandom --num=15000000 --cache_index_and_filter_blocks --bloom_bits=10 --threads=16 --cache_size=20000000 -partition_index_and_filters -batch_size=32 -multiread_batched -statistics --duration=20 2>&1 | egrep 'micros/op|block.cache.filter.hit|bloom.filter.(full|use)|number.multiget'
    multireadrandom :      26.403 micros/op 597517 ops/sec; (548427 of 671968 found)
    rocksdb.block.cache.filter.hit COUNT : 83443275
    rocksdb.bloom.filter.useful COUNT : 0
    rocksdb.bloom.filter.full.positive COUNT : 0
    rocksdb.bloom.filter.full.true.positive COUNT : 7931450
    rocksdb.number.multiget.get COUNT : 385984
    rocksdb.number.multiget.keys.read COUNT : 12351488
    rocksdb.number.multiget.bytes.read COUNT : 793145000
    rocksdb.number.multiget.keys.found COUNT : 7931450

After (middle performing run of three):

    $ ./db_bench_new --use-existing-db --benchmarks=multireadrandom --num=15000000 --cache_index_and_filter_blocks --bloom_bits=10 --threads=16 --cache_size=20000000 -partition_index_and_filters -batch_size=32 -multiread_batched -statistics --duration=20 2>&1 | egrep 'micros/op|block.cache.filter.hit|bloom.filter.(full|use)|number.multiget'
    multireadrandom :      21.024 micros/op 752963 ops/sec; (705188 of 863968 found)
    rocksdb.block.cache.filter.hit COUNT : 49856682
    rocksdb.bloom.filter.useful COUNT : 45684579
    rocksdb.bloom.filter.full.positive COUNT : 10395458
    rocksdb.bloom.filter.full.true.positive COUNT : 9908456
    rocksdb.number.multiget.get COUNT : 481984
    rocksdb.number.multiget.keys.read COUNT : 15423488
    rocksdb.number.multiget.bytes.read COUNT : 990845600
    rocksdb.number.multiget.keys.found COUNT : 9908456

So that's about 25% higher throughput even for random keys
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6757

Test Plan: unit test included

Reviewed By: anand1976

Differential Revision: D21243256

Pulled By: pdillinger

fbshipit-source-id: 5644a1468d9e8c8575be02f4e04bc5d62dbbb57f

HISTORY.md

@@ -25,8 +25,10 @@
 ### Bug Fixes
 * Fix a bug when making options.bottommost_compression, options.compression_opts and options.bottommost_compression_opts dynamically changeable: the modified values are not written to option files or returned back to users when being queried.
 * Fix a bug where index key comparisons were unaccounted in `PerfContext::user_key_comparison_count` for lookups in files written with `format_version >= 3`.
+* Fix many bloom.filter statistics not being updated in batch MultiGet.
 
 ### Performance Improvements
+* Improve performance of batch MultiGet with partitioned filters, by sharing block cache lookups to applicable filter blocks.
 * Reduced memory copies when fetching and uncompressing compressed blocks from sst files.
 
 ## 6.9.0 (03/29/2020)

db/db_bloom_filter_test.cc

@@ -1030,6 +1030,204 @@ TEST_F(DBBloomFilterTest, MemtablePrefixBloomOutOfDomain) {
   ASSERT_EQ(kKey, iter->key());
 }
 
+class DBBloomFilterTestVaryPrefixAndFormatVer
+    : public DBTestBase,
+      public testing::WithParamInterface<std::tuple<bool, uint32_t>> {
+ protected:
+  bool use_prefix_;
+  uint32_t format_version_;
+
+ public:
+  DBBloomFilterTestVaryPrefixAndFormatVer()
+      : DBTestBase("/db_bloom_filter_tests") {}
+
+  ~DBBloomFilterTestVaryPrefixAndFormatVer() override {}
+
+  void SetUp() override {
+    use_prefix_ = std::get<0>(GetParam());
+    format_version_ = std::get<1>(GetParam());
+  }
+
+  static std::string UKey(uint32_t i) { return Key(static_cast<int>(i)); }
+};
+
+TEST_P(DBBloomFilterTestVaryPrefixAndFormatVer, PartitionedMultiGet) {
+  Options options = CurrentOptions();
+  if (use_prefix_) {
+    // Entire key from UKey()
+    options.prefix_extractor.reset(NewCappedPrefixTransform(9));
+  }
+  options.statistics = ROCKSDB_NAMESPACE::CreateDBStatistics();
+  BlockBasedTableOptions bbto;
+  bbto.filter_policy.reset(NewBloomFilterPolicy(20));
+  bbto.partition_filters = true;
+  bbto.index_type = BlockBasedTableOptions::IndexType::kTwoLevelIndexSearch;
+  bbto.whole_key_filtering = !use_prefix_;
+  bbto.metadata_block_size = 128;
+  options.table_factory.reset(NewBlockBasedTableFactory(bbto));
+  DestroyAndReopen(options);
+  ReadOptions ropts;
+
+  constexpr uint32_t N = 10000;
+  // Add N/2 evens
+  for (uint32_t i = 0; i < N; i += 2) {
+    ASSERT_OK(Put(UKey(i), UKey(i)));
+  }
+  ASSERT_OK(Flush());
+  ASSERT_EQ(TotalTableFiles(), 1);
+
+  constexpr uint32_t Q = 29;
+  // MultiGet In
+  std::array<std::string, Q> keys;
+  std::array<Slice, Q> key_slices;
+  std::array<ColumnFamilyHandle*, Q> column_families;
+  // MultiGet Out
+  std::array<Status, Q> statuses;
+  std::array<PinnableSlice, Q> values;
+
+  TestGetAndResetTickerCount(options, BLOCK_CACHE_FILTER_HIT);
+  TestGetAndResetTickerCount(options, BLOCK_CACHE_FILTER_MISS);
+  TestGetAndResetTickerCount(options, BLOOM_FILTER_PREFIX_USEFUL);
+  TestGetAndResetTickerCount(options, BLOOM_FILTER_USEFUL);
+  TestGetAndResetTickerCount(options, BLOOM_FILTER_PREFIX_CHECKED);
+  TestGetAndResetTickerCount(options, BLOOM_FILTER_FULL_POSITIVE);
+  TestGetAndResetTickerCount(options, BLOOM_FILTER_FULL_TRUE_POSITIVE);
+
+  // Check that initial clump of keys only loads one partition filter from
+  // block cache.
+  // And that spread out keys load many partition filters.
+  // In both cases, mix present vs. not present keys.
+  for (uint32_t stride : {uint32_t{1}, (N / Q) | 1}) {
+    for (uint32_t i = 0; i < Q; ++i) {
+      keys[i] = UKey(i * stride);
+      key_slices[i] = Slice(keys[i]);
+      column_families[i] = db_->DefaultColumnFamily();
+      statuses[i] = Status();
+      values[i] = PinnableSlice();
+    }
+
+    db_->MultiGet(ropts, Q, &column_families[0], &key_slices[0], &values[0],
+                  /*timestamps=*/nullptr, &statuses[0], true);
+
+    // Confirm correct status results
+    uint32_t number_not_found = 0;
+    for (uint32_t i = 0; i < Q; ++i) {
+      if ((i * stride % 2) == 0) {
+        ASSERT_OK(statuses[i]);
+      } else {
+        ASSERT_TRUE(statuses[i].IsNotFound());
+        ++number_not_found;
+      }
+    }
+
+    // Confirm correct Bloom stats (no FPs)
+    uint64_t filter_useful = TestGetAndResetTickerCount(
+        options,
+        use_prefix_ ? BLOOM_FILTER_PREFIX_USEFUL : BLOOM_FILTER_USEFUL);
+    uint64_t filter_checked =
+        TestGetAndResetTickerCount(options, use_prefix_
+                                                ? BLOOM_FILTER_PREFIX_CHECKED
+                                                : BLOOM_FILTER_FULL_POSITIVE) +
+        (use_prefix_ ? 0 : filter_useful);
+    EXPECT_EQ(filter_useful, number_not_found);
+    EXPECT_EQ(filter_checked, Q);
+    if (!use_prefix_) {
+      EXPECT_EQ(
+          TestGetAndResetTickerCount(options, BLOOM_FILTER_FULL_TRUE_POSITIVE),
+          Q - number_not_found);
+    }
+
+    // Confirm no duplicate loading same filter partition
+    uint64_t filter_accesses =
+        TestGetAndResetTickerCount(options, BLOCK_CACHE_FILTER_HIT) +
+        TestGetAndResetTickerCount(options, BLOCK_CACHE_FILTER_MISS);
+    if (stride == 1) {
+      EXPECT_EQ(filter_accesses, 1);
+    } else {
+      // for large stride
+      EXPECT_GE(filter_accesses, Q / 2 + 1);
+    }
+  }
+
+  // Check that a clump of keys (present and not) works when spanning
+  // two partitions
+  int found_spanning = 0;
+  for (uint32_t start = 0; start < N / 2;) {
+    for (uint32_t i = 0; i < Q; ++i) {
+      keys[i] = UKey(start + i);
+      key_slices[i] = Slice(keys[i]);
+      column_families[i] = db_->DefaultColumnFamily();
+      statuses[i] = Status();
+      values[i] = PinnableSlice();
+    }
+
+    db_->MultiGet(ropts, Q, &column_families[0], &key_slices[0], &values[0],
+                  /*timestamps=*/nullptr, &statuses[0], true);
+
+    // Confirm correct status results
+    uint32_t number_not_found = 0;
+    for (uint32_t i = 0; i < Q; ++i) {
+      if (((start + i) % 2) == 0) {
+        ASSERT_OK(statuses[i]);
+      } else {
+        ASSERT_TRUE(statuses[i].IsNotFound());
+        ++number_not_found;
+      }
+    }
+
+    // Confirm correct Bloom stats (might see some FPs)
+    uint64_t filter_useful = TestGetAndResetTickerCount(
+        options,
+        use_prefix_ ? BLOOM_FILTER_PREFIX_USEFUL : BLOOM_FILTER_USEFUL);
+    uint64_t filter_checked =
+        TestGetAndResetTickerCount(options, use_prefix_
+                                                ? BLOOM_FILTER_PREFIX_CHECKED
+                                                : BLOOM_FILTER_FULL_POSITIVE) +
+        (use_prefix_ ? 0 : filter_useful);
+    EXPECT_GE(filter_useful, number_not_found - 2);  // possible FP
+    EXPECT_EQ(filter_checked, Q);
+    if (!use_prefix_) {
+      EXPECT_EQ(
+          TestGetAndResetTickerCount(options, BLOOM_FILTER_FULL_TRUE_POSITIVE),
+          Q - number_not_found);
+    }
+
+    // Confirm no duplicate loading of same filter partition
+    uint64_t filter_accesses =
+        TestGetAndResetTickerCount(options, BLOCK_CACHE_FILTER_HIT) +
+        TestGetAndResetTickerCount(options, BLOCK_CACHE_FILTER_MISS);
+    if (filter_accesses == 2) {
+      // Spanned across partitions.
+      ++found_spanning;
+      if (found_spanning >= 2) {
+        break;
+      } else {
+        // Ensure that at least once we have at least one present and
+        // one non-present key on both sides of partition boundary.
+        start += 2;
+      }
+    } else {
+      EXPECT_EQ(filter_accesses, 1);
+      // See explanation at "start += 2"
+      start += Q - 4;
+    }
+  }
+  EXPECT_TRUE(found_spanning >= 2);
+}
+
+INSTANTIATE_TEST_CASE_P(DBBloomFilterTestVaryPrefixAndFormatVer,
+                        DBBloomFilterTestVaryPrefixAndFormatVer,
+                        ::testing::Values(
+                            // (use_prefix, format_version)
+                            std::make_tuple(false, 2),
+                            std::make_tuple(false, 3),
+                            std::make_tuple(false, 4),
+                            std::make_tuple(false, 5),
+                            std::make_tuple(true, 2),
+                            std::make_tuple(true, 3),
+                            std::make_tuple(true, 4),
+                            std::make_tuple(true, 5)));
+
 #ifndef ROCKSDB_LITE
 namespace {
 namespace BFP2 {

table/block_based/block_based_table_reader.cc

@@ -2147,14 +2147,37 @@ void BlockBasedTable::FullFilterKeysMayMatch(
   if (filter == nullptr || filter->IsBlockBased()) {
     return;
   }
+  uint64_t before_keys = range->KeysLeft();
+  assert(before_keys > 0);  // Caller should ensure
   if (rep_->whole_key_filtering) {
     filter->KeysMayMatch(range, prefix_extractor, kNotValid, no_io,
                          lookup_context);
+    uint64_t after_keys = range->KeysLeft();
+    if (after_keys) {
+      RecordTick(rep_->ioptions.statistics, BLOOM_FILTER_FULL_POSITIVE,
+                 after_keys);
+      PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_full_positive, after_keys,
+                                rep_->level);
+    }
+    uint64_t filtered_keys = before_keys - after_keys;
+    if (filtered_keys) {
+      RecordTick(rep_->ioptions.statistics, BLOOM_FILTER_USEFUL, filtered_keys);
+      PERF_COUNTER_BY_LEVEL_ADD(bloom_filter_useful, filtered_keys,
+                                rep_->level);
+    }
   } else if (!read_options.total_order_seek && prefix_extractor &&
              rep_->table_properties->prefix_extractor_name.compare(
                  prefix_extractor->Name()) == 0) {
     filter->PrefixesMayMatch(range, prefix_extractor, kNotValid, false,
                              lookup_context);
+    RecordTick(rep_->ioptions.statistics, BLOOM_FILTER_PREFIX_CHECKED,
+               before_keys);
+    uint64_t after_keys = range->KeysLeft();
+    uint64_t filtered_keys = before_keys - after_keys;
+    if (filtered_keys) {
+      RecordTick(rep_->ioptions.statistics, BLOOM_FILTER_PREFIX_USEFUL,
+                 filtered_keys);
+    }
   }
 }
 
@@ -2342,6 +2365,12 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
                                const MultiGetRange* mget_range,
                                const SliceTransform* prefix_extractor,
                                bool skip_filters) {
+  if (mget_range->empty()) {
+    // Caller should ensure non-empty (performance bug)
+    assert(false);
+    return;  // Nothing to do
+  }
+
   FilterBlockReader* const filter =
       !skip_filters ? rep_->filter.get() : nullptr;
   MultiGetRange sst_file_range(*mget_range, mget_range->begin(),
@@ -2351,7 +2380,7 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
   // If full filter not useful, Then go into each block
   const bool no_io = read_options.read_tier == kBlockCacheTier;
   uint64_t tracing_mget_id = BlockCacheTraceHelper::kReservedGetId;
-  if (!sst_file_range.empty() && sst_file_range.begin()->get_context) {
+  if (sst_file_range.begin()->get_context) {
     tracing_mget_id = sst_file_range.begin()->get_context->get_tracing_get_id();
   }
   BlockCacheLookupContext lookup_context{
@@ -2360,7 +2389,7 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
   FullFilterKeysMayMatch(read_options, filter, &sst_file_range, no_io,
                          prefix_extractor, &lookup_context);
 
-  if (skip_filters || !sst_file_range.empty()) {
+  if (!sst_file_range.empty()) {
     IndexBlockIter iiter_on_stack;
     // if prefix_extractor found in block differs from options, disable
     // BlockPrefixIndex. Only do this check when index_type is kHashSearch.

table/block_based/full_filter_block.cc

@@ -192,7 +192,6 @@ void FullFilterBlockReader::KeysMayMatch(
     uint64_t block_offset, const bool no_io,
     BlockCacheLookupContext* lookup_context) {
 #ifdef NDEBUG
-  (void)range;
   (void)block_offset;
 #endif
   assert(block_offset == kNotValid);
@@ -209,7 +208,6 @@ void FullFilterBlockReader::PrefixesMayMatch(
     uint64_t block_offset, const bool no_io,
     BlockCacheLookupContext* lookup_context) {
 #ifdef NDEBUG
-  (void)range;
   (void)block_offset;
 #endif
   assert(block_offset == kNotValid);

table/block_based/partitioned_filter_block.cc

@@ -172,13 +172,23 @@ bool PartitionedFilterBlockReader::KeyMayMatch(
                   &FullFilterBlockReader::KeyMayMatch);
 }
 
+void PartitionedFilterBlockReader::KeysMayMatch(
+    MultiGetRange* range, const SliceTransform* prefix_extractor,
+    uint64_t block_offset, const bool no_io,
+    BlockCacheLookupContext* lookup_context) {
+  assert(block_offset == kNotValid);
+  if (!whole_key_filtering()) {
+    return;  // Any/all may match
+  }
+
+  MayMatch(range, prefix_extractor, block_offset, no_io, lookup_context,
+           &FullFilterBlockReader::KeysMayMatch);
+}
+
 bool PartitionedFilterBlockReader::PrefixMayMatch(
     const Slice& prefix, const SliceTransform* prefix_extractor,
     uint64_t block_offset, const bool no_io, const Slice* const const_ikey_ptr,
     GetContext* get_context, BlockCacheLookupContext* lookup_context) {
-#ifdef NDEBUG
-  (void)block_offset;
-#endif
   assert(const_ikey_ptr != nullptr);
   assert(block_offset == kNotValid);
   if (!table_prefix_extractor() && !prefix_extractor) {
@@ -190,6 +200,19 @@ bool PartitionedFilterBlockReader::PrefixMayMatch(
                   &FullFilterBlockReader::PrefixMayMatch);
 }
 
+void PartitionedFilterBlockReader::PrefixesMayMatch(
+    MultiGetRange* range, const SliceTransform* prefix_extractor,
+    uint64_t block_offset, const bool no_io,
+    BlockCacheLookupContext* lookup_context) {
+  assert(block_offset == kNotValid);
+  if (!table_prefix_extractor() && !prefix_extractor) {
+    return;  // Any/all may match
+  }
+
+  MayMatch(range, prefix_extractor, block_offset, no_io, lookup_context,
+           &FullFilterBlockReader::PrefixesMayMatch);
+}
+
 BlockHandle PartitionedFilterBlockReader::GetFilterPartitionHandle(
     const CachableEntry<Block>& filter_block, const Slice& entry) const {
   IndexBlockIter iter;
@@ -285,6 +308,79 @@ bool PartitionedFilterBlockReader::MayMatch(
       lookup_context);
 }
 
+void PartitionedFilterBlockReader::MayMatch(
+    MultiGetRange* range, const SliceTransform* prefix_extractor,
+    uint64_t block_offset, bool no_io, BlockCacheLookupContext* lookup_context,
+    FilterManyFunction filter_function) const {
+  CachableEntry<Block> filter_block;
+  Status s = GetOrReadFilterBlock(no_io, range->begin()->get_context,
+                                  lookup_context, &filter_block);
+  if (UNLIKELY(!s.ok())) {
+    IGNORE_STATUS_IF_ERROR(s);
+    return;  // Any/all may match
+  }
+
+  if (UNLIKELY(filter_block.GetValue()->size() == 0)) {
+    return;  // Any/all may match
+  }
+
+  auto start_iter_same_handle = range->begin();
+  BlockHandle prev_filter_handle = BlockHandle::NullBlockHandle();
+
+  // For all keys mapping to same partition (must be adjacent in sorted order)
+  // share block cache lookup and use full filter multiget on the partition
+  // filter.
+  for (auto iter = start_iter_same_handle; iter != range->end(); ++iter) {
+    // TODO: re-use one top-level index iterator
+    BlockHandle this_filter_handle =
+        GetFilterPartitionHandle(filter_block, iter->ikey);
+    if (!prev_filter_handle.IsNull() &&
+        this_filter_handle != prev_filter_handle) {
+      MultiGetRange subrange(*range, start_iter_same_handle, iter);
+      MayMatchPartition(&subrange, prefix_extractor, block_offset,
+                        prev_filter_handle, no_io, lookup_context,
+                        filter_function);
+      range->AddSkipsFrom(subrange);
+      start_iter_same_handle = iter;
+    }
+    if (UNLIKELY(this_filter_handle.size() == 0)) {  // key is out of range
+      // Not reachable with current behavior of GetFilterPartitionHandle
+      assert(false);
+      range->SkipKey(iter);
+      prev_filter_handle = BlockHandle::NullBlockHandle();
+    } else {
+      prev_filter_handle = this_filter_handle;
+    }
+  }
+  if (!prev_filter_handle.IsNull()) {
+    MultiGetRange subrange(*range, start_iter_same_handle, range->end());
+    MayMatchPartition(&subrange, prefix_extractor, block_offset,
+                      prev_filter_handle, no_io, lookup_context,
+                      filter_function);
+    range->AddSkipsFrom(subrange);
+  }
+}
+
+void PartitionedFilterBlockReader::MayMatchPartition(
+    MultiGetRange* range, const SliceTransform* prefix_extractor,
+    uint64_t block_offset, BlockHandle filter_handle, bool no_io,
+    BlockCacheLookupContext* lookup_context,
+    FilterManyFunction filter_function) const {
+  CachableEntry<ParsedFullFilterBlock> filter_partition_block;
+  Status s = GetFilterPartitionBlock(
+      nullptr /* prefetch_buffer */, filter_handle, no_io,
+      range->begin()->get_context, lookup_context, &filter_partition_block);
+  if (UNLIKELY(!s.ok())) {
+    IGNORE_STATUS_IF_ERROR(s);
+    return;  // Any/all may match
+  }
+
+  FullFilterBlockReader filter_partition(table(),
+                                         std::move(filter_partition_block));
+  (filter_partition.*filter_function)(range, prefix_extractor, block_offset,
+                                      no_io, lookup_context);
+}
+
 size_t PartitionedFilterBlockReader::ApproximateMemoryUsage() const {
   size_t usage = ApproximateFilterBlockMemoryUsage();
 #ifdef ROCKSDB_MALLOC_USABLE_SIZE

table/block_based/partitioned_filter_block.h

@@ -80,12 +80,21 @@ class PartitionedFilterBlockReader : public FilterBlockReaderCommon<Block> {
                    uint64_t block_offset, const bool no_io,
                    const Slice* const const_ikey_ptr, GetContext* get_context,
                    BlockCacheLookupContext* lookup_context) override;
+  void KeysMayMatch(MultiGetRange* range,
+                    const SliceTransform* prefix_extractor,
+                    uint64_t block_offset, const bool no_io,
+                    BlockCacheLookupContext* lookup_context) override;
+
   bool PrefixMayMatch(const Slice& prefix,
                       const SliceTransform* prefix_extractor,
                       uint64_t block_offset, const bool no_io,
                       const Slice* const const_ikey_ptr,
                       GetContext* get_context,
                       BlockCacheLookupContext* lookup_context) override;
+  void PrefixesMayMatch(MultiGetRange* range,
+                        const SliceTransform* prefix_extractor,
+                        uint64_t block_offset, const bool no_io,
+                        BlockCacheLookupContext* lookup_context) override;
 
   size_t ApproximateMemoryUsage() const override;
 
@@ -108,6 +117,19 @@ class PartitionedFilterBlockReader : public FilterBlockReaderCommon<Block> {
                 GetContext* get_context,
                 BlockCacheLookupContext* lookup_context,
                 FilterFunction filter_function) const;
+  using FilterManyFunction = void (FullFilterBlockReader::*)(
+      MultiGetRange* range, const SliceTransform* prefix_extractor,
+      uint64_t block_offset, const bool no_io,
+      BlockCacheLookupContext* lookup_context);
+  void MayMatch(MultiGetRange* range, const SliceTransform* prefix_extractor,
+                uint64_t block_offset, bool no_io,
+                BlockCacheLookupContext* lookup_context,
+                FilterManyFunction filter_function) const;
+  void MayMatchPartition(MultiGetRange* range,
+                         const SliceTransform* prefix_extractor,
+                         uint64_t block_offset, BlockHandle filter_handle,
+                         bool no_io, BlockCacheLookupContext* lookup_context,
+                         FilterManyFunction filter_function) const;
   void CacheDependencies(bool pin) override;
 
   const InternalKeyComparator* internal_comparator() const;

table/format.h

@@ -38,6 +38,8 @@ const int kMagicNumberLengthByte = 8;
 // block or a meta block.
 class BlockHandle {
  public:
+  // Creates a block handle with special values indicating "uninitialized,"
+  // distinct from the "null" block handle.
   BlockHandle();
   BlockHandle(uint64_t offset, uint64_t size);
 
@@ -65,6 +67,13 @@ class BlockHandle {
   // Maximum encoding length of a BlockHandle
   enum { kMaxEncodedLength = 10 + 10 };
 
+  inline bool operator==(const BlockHandle& rhs) const {
+    return offset_ == rhs.offset_ && size_ == rhs.size_;
+  }
+  inline bool operator!=(const BlockHandle& rhs) const {
+    return !(*this == rhs);
+  }
+
  private:
   uint64_t offset_;
   uint64_t size_;

table/multiget_context.h

@@ -13,6 +13,7 @@
 #include "rocksdb/statistics.h"
 #include "rocksdb/types.h"
 #include "util/autovector.h"
+#include "util/math.h"
 
 namespace ROCKSDB_NAMESPACE {
 class GetContext;
@@ -157,7 +158,7 @@ class MultiGetContext {
       Iterator(const Range* range, size_t idx)
           : range_(range), ctx_(range->ctx_), index_(idx) {
         while (index_ < range_->end_ &&
-               (1ull << index_) &
+               (uint64_t{1} << index_) &
                    (range_->ctx_->value_mask_ | range_->skip_mask_))
           index_++;
       }
@@ -167,7 +168,7 @@ class MultiGetContext {
 
       Iterator& operator++() {
         while (++index_ < range_->end_ &&
-               (1ull << index_) &
+               (uint64_t{1} << index_) &
                    (range_->ctx_->value_mask_ | range_->skip_mask_))
           ;
         return *this;
@@ -209,6 +210,8 @@ class MultiGetContext {
       start_ = first.index_;
       end_ = last.index_;
       skip_mask_ = mget_range.skip_mask_;
+      assert(start_ < 64);
+      assert(end_ < 64);
     }
 
     Range() = default;
@@ -217,31 +220,27 @@ class MultiGetContext {
 
     Iterator end() const { return Iterator(this, end_); }
 
-    bool empty() {
+    bool empty() const { return RemainingMask() == 0; }
-      return (((1ull << end_) - 1) & ~((1ull << start_) - 1) &
-              ~(ctx_->value_mask_ | skip_mask_)) == 0;
-    }
 
-    void SkipKey(const Iterator& iter) { skip_mask_ |= 1ull << iter.index_; }
+    void SkipKey(const Iterator& iter) {
+      skip_mask_ |= uint64_t{1} << iter.index_;
+    }
 
     // Update the value_mask_ in MultiGetContext so its
     // immediately reflected in all the Range Iterators
     void MarkKeyDone(Iterator& iter) {
-      ctx_->value_mask_ |= (1ull << iter.index_);
+      ctx_->value_mask_ |= (uint64_t{1} << iter.index_);
     }
 
-    bool CheckKeyDone(Iterator& iter) {
+    bool CheckKeyDone(Iterator& iter) const {
-      return ctx_->value_mask_ & (1ull << iter.index_);
+      return ctx_->value_mask_ & (uint64_t{1} << iter.index_);
     }
 
-    uint64_t KeysLeft() {
+    uint64_t KeysLeft() const { return BitsSetToOne(RemainingMask()); }
-      uint64_t new_val = skip_mask_ | ctx_->value_mask_;
+
-      uint64_t count = 0;
+    void AddSkipsFrom(const Range& other) {
-      while (new_val) {
+      assert(ctx_ == other.ctx_);
-        new_val = new_val & (new_val - 1);
+      skip_mask_ |= other.skip_mask_;
-        count++;
-      }
-      return end_ - count;
     }
 
    private:
@@ -252,7 +251,14 @@ class MultiGetContext {
     uint64_t skip_mask_;
 
     Range(MultiGetContext* ctx, size_t num_keys)
-        : ctx_(ctx), start_(0), end_(num_keys), skip_mask_(0) {}
+        : ctx_(ctx), start_(0), end_(num_keys), skip_mask_(0) {
+      assert(num_keys < 64);
+    }
+
+    uint64_t RemainingMask() const {
+      return (((uint64_t{1} << end_) - 1) & ~((uint64_t{1} << start_) - 1) &
+              ~(ctx_->value_mask_ | skip_mask_));
+    }
   };
 
   // Return the initial range that encompasses all the keys in the batch

util/math.h

@@ -0,0 +1,38 @@
+//  Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+
+#pragma once
+
+#include <assert.h>
+#include <stdint.h>
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+namespace ROCKSDB_NAMESPACE {
+
+template <typename T>
+inline int BitsSetToOne(T v) {
+  static_assert(std::is_integral<T>::value, "non-integral type");
+#ifdef _MSC_VER
+  static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
+  if (sizeof(T) > sizeof(uint32_t)) {
+    return static_cast<int>(__popcnt64(static_cast<uint64_t>(v)));
+  } else {
+    return static_cast<int>(__popcnt(static_cast<uint32_t>(v)));
+  }
+#else
+  static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
+  if (sizeof(T) > sizeof(unsigned long)) {
+    return __builtin_popcountll(static_cast<unsigned long long>(v));
+  } else if (sizeof(T) > sizeof(unsigned int)) {
+    return __builtin_popcountl(static_cast<unsigned long>(v));
+  } else {
+    return __builtin_popcount(static_cast<unsigned int>(v));
+  }
+#endif
+}
+
+}  // namespace ROCKSDB_NAMESPACE