Reduce iterator key comparison for upper/lower bound check (#5111)

Summary:
Previously if iterator upper/lower bound presents, `DBIter` will check the bound for every key. This patch turns the check into per-file or per-data block check when applicable, by checking against either file largest/smallest key or block index key.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5111

Differential Revision: D15330061

Pulled By: siying

fbshipit-source-id: 8a653fe3cd50d94d81eb2d13b087326c58ee2024

HISTORY.md

@@ -11,6 +11,7 @@
 * Reduce binary search when iterator reseek into the same data block.
 * DBIter::Next() can skip user key checking if previous entry's seqnum is 0.
 * Merging iterator to avoid child iterator reseek for some cases
+* Reduce iterator key comparision for upper/lower bound check.
 
 ### Bug Fixes
 

db/db_iter.cc

@@ -467,7 +467,7 @@ inline bool DBIter::FindNextUserEntryInternal(bool skipping, bool prefix_check)
 
     is_key_seqnum_zero_ = (ikey_.sequence == 0);
 
-    if (iterate_upper_bound_ != nullptr &&
+    if (iterate_upper_bound_ != nullptr && iter_.MayBeOutOfUpperBound() &&
         user_comparator_.Compare(ikey_.user_key, *iterate_upper_bound_) >= 0) {
       break;
     }
@@ -859,7 +859,7 @@ void DBIter::PrevInternal() {
       return;
     }
 
-    if (iterate_lower_bound_ != nullptr &&
+    if (iterate_lower_bound_ != nullptr && iter_.MayBeOutOfLowerBound() &&
         user_comparator_.Compare(saved_key_.GetUserKey(),
                                  *iterate_lower_bound_) < 0) {
       // We've iterated earlier than the user-specified lower bound.

db/version_set.cc

@@ -887,7 +887,7 @@ class LevelIterator final : public InternalIterator {
   void SeekToFirst() override;
   void SeekToLast() override;
   void Next() final override;
-  bool NextAndGetResult(Slice* ret_key) override;
+  bool NextAndGetResult(IterateResult* result) override;
   void Prev() override;
 
   bool Valid() const override { return file_iter_.Valid(); }
@@ -895,23 +895,38 @@ class LevelIterator final : public InternalIterator {
     assert(Valid());
     return file_iter_.key();
   }
+
   Slice value() const override {
     assert(Valid());
     return file_iter_.value();
   }
+
   Status status() const override {
     return file_iter_.iter() ? file_iter_.status() : Status::OK();
   }
+
+  inline bool MayBeOutOfLowerBound() override {
+    assert(Valid());
+    return may_be_out_of_lower_bound_ && file_iter_.MayBeOutOfLowerBound();
+  }
+
+  inline bool MayBeOutOfUpperBound() override {
+    assert(Valid());
+    return file_iter_.MayBeOutOfUpperBound();
+  }
+
   void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) override {
     pinned_iters_mgr_ = pinned_iters_mgr;
     if (file_iter_.iter()) {
       file_iter_.SetPinnedItersMgr(pinned_iters_mgr);
     }
   }
+
   bool IsKeyPinned() const override {
     return pinned_iters_mgr_ && pinned_iters_mgr_->PinningEnabled() &&
            file_iter_.iter() && file_iter_.IsKeyPinned();
   }
+
   bool IsValuePinned() const override {
     return pinned_iters_mgr_ && pinned_iters_mgr_->PinningEnabled() &&
            file_iter_.iter() && file_iter_.IsValuePinned();
@@ -954,12 +969,16 @@ class LevelIterator final : public InternalIterator {
       smallest_compaction_key = (*compaction_boundaries_)[file_index_].smallest;
       largest_compaction_key = (*compaction_boundaries_)[file_index_].largest;
     }
+    may_be_out_of_lower_bound_ =
+        read_options_.iterate_lower_bound != nullptr &&
+        user_comparator_.Compare(ExtractUserKey(file_smallest_key(file_index_)),
+                                 *read_options_.iterate_lower_bound) < 0;
     return table_cache_->NewIterator(
         read_options_, env_options_, icomparator_, *file_meta.file_metadata,
         range_del_agg_, prefix_extractor_,
-        nullptr /* don't need reference to table */,
-        file_read_hist_, for_compaction_, nullptr /* arena */, skip_filters_,
-        level_, smallest_compaction_key, largest_compaction_key);
+        nullptr /* don't need reference to table */, file_read_hist_,
+        for_compaction_, nullptr /* arena */, skip_filters_, level_,
+        smallest_compaction_key, largest_compaction_key);
   }
 
   TableCache* table_cache_;
@@ -975,6 +994,7 @@ class LevelIterator final : public InternalIterator {
   bool should_sample_;
   bool for_compaction_;
   bool skip_filters_;
+  bool may_be_out_of_lower_bound_ = true;
   size_t file_index_;
   int level_;
   RangeDelAggregator* range_del_agg_;
@@ -1043,11 +1063,12 @@ void LevelIterator::SeekToLast() {
 
 void LevelIterator::Next() { NextImpl(); }
 
-bool LevelIterator::NextAndGetResult(Slice* ret_key) {
+bool LevelIterator::NextAndGetResult(IterateResult* result) {
   NextImpl();
   bool is_valid = Valid();
   if (is_valid) {
-    *ret_key = key();
+    result->key = key();
+    result->may_be_out_of_upper_bound = MayBeOutOfUpperBound();
   }
   return is_valid;
 }
@@ -4278,10 +4299,9 @@ Status VersionSet::Recover(
         ", last_sequence is %" PRIu64 ", log_number is %" PRIu64
         ",prev_log_number is %" PRIu64 ",max_column_family is %" PRIu32
         ",min_log_number_to_keep is %" PRIu64 "\n",
-        manifest_path.c_str(), manifest_file_number_,
-        next_file_number_.load(), last_sequence_.load(), log_number,
-        prev_log_number_, column_family_set_->GetMaxColumnFamily(),
-        min_log_number_to_keep_2pc());
+        manifest_path.c_str(), manifest_file_number_, next_file_number_.load(),
+        last_sequence_.load(), log_number, prev_log_number_,
+        column_family_set_->GetMaxColumnFamily(), min_log_number_to_keep_2pc());
 
     for (auto cfd : *column_family_set_) {
       if (cfd->IsDropped()) {

table/block_based_table_reader.cc

@@ -2446,11 +2446,12 @@ void BlockBasedTableIterator<TBlockIter, TValue>::Next() {
 
 template <class TBlockIter, typename TValue>
 bool BlockBasedTableIterator<TBlockIter, TValue>::NextAndGetResult(
-    Slice* ret_key) {
+    IterateResult* result) {
   Next();
   bool is_valid = Valid();
   if (is_valid) {
-    *ret_key = key();
+    result->key = key();
+    result->may_be_out_of_upper_bound = MayBeOutOfUpperBound();
   }
   return is_valid;
 }
@@ -2531,6 +2532,11 @@ void BlockBasedTableIterator<TBlockIter, TValue>::InitDataBlock() {
         key_includes_seq_, index_key_is_full_,
         /* get_context */ nullptr, s, prefetch_buffer_.get());
     block_iter_points_to_real_block_ = true;
+    if (read_options_.iterate_upper_bound != nullptr) {
+      data_block_within_upper_bound_ =
+          (user_comparator_.Compare(*read_options_.iterate_upper_bound,
+                                    index_iter_->user_key()) > 0);
+    }
   }
 }
 
@@ -2543,13 +2549,9 @@ void BlockBasedTableIterator<TBlockIter, TValue>::FindBlockForward() {
       return;
     }
     // Whether next data block is out of upper bound, if there is one.
-    bool next_block_is_out_of_bound = false;
-    if (read_options_.iterate_upper_bound != nullptr &&
-        block_iter_points_to_real_block_) {
-      next_block_is_out_of_bound =
-          (user_comparator_.Compare(*read_options_.iterate_upper_bound,
-                                    index_iter_->user_key()) <= 0);
-    }
+    bool next_block_is_out_of_bound =
+        read_options_.iterate_upper_bound != nullptr &&
+        block_iter_points_to_real_block_ && !data_block_within_upper_bound_;
     ResetDataIter();
     index_iter_->Next();
     if (next_block_is_out_of_bound) {

table/block_based_table_reader.h

@@ -588,7 +588,7 @@ class BlockBasedTableIterator : public InternalIteratorBase<TValue> {
   void SeekToFirst() override;
   void SeekToLast() override;
   void Next() final override;
-  bool NextAndGetResult(Slice* ret_key) override;
+  bool NextAndGetResult(IterateResult* result) override;
   void Prev() override;
   bool Valid() const override {
     return !is_out_of_bound_ && block_iter_points_to_real_block_ &&
@@ -619,6 +619,11 @@ class BlockBasedTableIterator : public InternalIteratorBase<TValue> {
   // Whether iterator invalidated for being out of bound.
   bool IsOutOfBound() override { return is_out_of_bound_; }
 
+  inline bool MayBeOutOfUpperBound() override {
+    assert(Valid());
+    return !data_block_within_upper_bound_;
+  }
+
   void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) override {
     pinned_iters_mgr_ = pinned_iters_mgr;
   }
@@ -680,6 +685,8 @@ class BlockBasedTableIterator : public InternalIteratorBase<TValue> {
   TBlockIter block_iter_;
   bool block_iter_points_to_real_block_;
   bool is_out_of_bound_ = false;
+  // Whether current data block being fully within iterate upper bound.
+  bool data_block_within_upper_bound_ = false;
   bool check_filter_;
   // TODO(Zhongyi): pick a better name
   bool need_upper_bound_check_;

table/internal_iterator.h

@@ -17,6 +17,11 @@ namespace rocksdb {
 
 class PinnedIteratorsManager;
 
+struct IterateResult {
+  Slice key;
+  bool may_be_out_of_upper_bound;
+};
+
 template <class TValue>
 class InternalIteratorBase : public Cleanable {
  public:
@@ -55,11 +60,20 @@ class InternalIteratorBase : public Cleanable {
   // REQUIRES: Valid()
   virtual void Next() = 0;
 
-  virtual bool NextAndGetResult(Slice* ret_key) {
+  // Moves to the next entry in the source, and return result. Iterator
+  // implementation should override this method to help methods inline better,
+  // or when MayBeOutOfUpperBound() is non-trivial.
+  // REQUIRES: Valid()
+  virtual bool NextAndGetResult(IterateResult* result) {
     Next();
     bool is_valid = Valid();
     if (is_valid) {
-      *ret_key = key();
+      result->key = key();
+      // Default may_be_out_of_upper_bound to true to avoid unnecessary virtual
+      // call. If an implementation has non-trivial MayBeOutOfUpperBound(),
+      // it should also override NextAndGetResult().
+      result->may_be_out_of_upper_bound = true;
+      assert(MayBeOutOfUpperBound());
     }
     return is_valid;
   }
@@ -94,6 +108,13 @@ class InternalIteratorBase : public Cleanable {
   // upper bound
   virtual bool IsOutOfBound() { return false; }
 
+  // Keys return from this iterator can be smaller than iterate_lower_bound.
+  virtual bool MayBeOutOfLowerBound() { return true; }
+
+  // Keys return from this iterator can be larger or equal to
+  // iterate_upper_bound.
+  virtual bool MayBeOutOfUpperBound() { return true; }
+
   // Pass the PinnedIteratorsManager to the Iterator, most Iterators dont
   // communicate with PinnedIteratorsManager so default implementation is no-op
   // but for Iterators that need to communicate with PinnedIteratorsManager

table/iterator_wrapper.h

@@ -56,7 +56,10 @@ class IteratorWrapperBase {
 
   // Iterator interface methods
   bool Valid() const        { return valid_; }
-  Slice key() const         { assert(Valid()); return key_; }
+  Slice key() const {
+    assert(Valid());
+    return result_.key;
+  }
   TValue value() const {
     assert(Valid());
     return iter_->value();
@@ -65,7 +68,7 @@ class IteratorWrapperBase {
   Status status() const     { assert(iter_); return iter_->status(); }
   void Next() {
     assert(iter_);
-    valid_ = iter_->NextAndGetResult(&key_);
+    valid_ = iter_->NextAndGetResult(&result_);
     assert(!valid_ || iter_->status().ok());
   }
   void Prev()               { assert(iter_); iter_->Prev();        Update(); }
@@ -83,6 +86,16 @@ class IteratorWrapperBase {
   void SeekToFirst()        { assert(iter_); iter_->SeekToFirst(); Update(); }
   void SeekToLast()         { assert(iter_); iter_->SeekToLast();  Update(); }
 
+  bool MayBeOutOfLowerBound() {
+    assert(Valid());
+    return iter_->MayBeOutOfLowerBound();
+  }
+
+  bool MayBeOutOfUpperBound() {
+    assert(Valid());
+    return result_.may_be_out_of_upper_bound;
+  }
+
   void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) {
     assert(iter_);
     iter_->SetPinnedItersMgr(pinned_iters_mgr);
@@ -100,14 +113,15 @@ class IteratorWrapperBase {
   void Update() {
     valid_ = iter_->Valid();
     if (valid_) {
-      key_ = iter_->key();
       assert(iter_->status().ok());
+      result_.key = iter_->key();
+      result_.may_be_out_of_upper_bound = true;
     }
   }
 
   InternalIteratorBase<TValue>* iter_;
+  IterateResult result_;
   bool valid_;
-  Slice key_;
 };
 
 using IteratorWrapper = IteratorWrapperBase<Slice>;

table/merging_iterator.cc

@@ -227,6 +227,16 @@ class MergingIterator : public InternalIterator {
     current_ = CurrentForward();
   }
 
+  bool NextAndGetResult(IterateResult* result) override {
+    Next();
+    bool is_valid = Valid();
+    if (is_valid) {
+      result->key = key();
+      result->may_be_out_of_upper_bound = MayBeOutOfUpperBound();
+    }
+    return is_valid;
+  }
+
   void Prev() override {
     assert(Valid());
     // Ensure that all children are positioned before key().
@@ -296,6 +306,20 @@ class MergingIterator : public InternalIterator {
     return current_->value();
   }
 
+  // Here we simply relay MayBeOutOfLowerBound/MayBeOutOfUpperBound result
+  // from current child iterator. Potentially as long as one of child iterator
+  // report out of bound is not possible, we know current key is within bound.
+
+  bool MayBeOutOfLowerBound() override {
+    assert(Valid());
+    return current_->MayBeOutOfLowerBound();
+  }
+
+  bool MayBeOutOfUpperBound() override {
+    assert(Valid());
+    return current_->MayBeOutOfUpperBound();
+  }
+
   void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) override {
     pinned_iters_mgr_ = pinned_iters_mgr;
     for (auto& child : children_) {