Fixed and simplified merge_helper

Summary:
MergeUntil was not reporting a success when merging an operand with
a Value/Deletion despite the comments in MergeHelper and CompactionJob
indicating otherwise. This lead to operands being written to the compaction
output unnecessarily:

M1 M2 M3 P M4 M5 --> (P+M1+M2+M3) M2 M3 M4 M5 (before the diff)
M1 M2 M3 P M4 M5 --> (P+M1+M2+M3) M4 M5 (after the diff)

In addition, the code handling Values/Deletion was basically identical.
This patch unifies the code. Finally, this patch also adds testing for
merge_helper.

Test Plan: make && make check

Reviewers: sdong, rven, yhchiang, tnovak, igor

Reviewed By: igor

Subscribers: tnovak, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D42351

Makefile

@@ -252,6 +252,7 @@ TESTS = \
 	memenv_test \
 	mock_env_test \
 	memtable_list_test \
+	merge_helper_test \
 	merge_test \
 	merger_test \
 	redis_test \
@@ -805,6 +806,9 @@ write_batch_test: db/write_batch_test.o $(LIBOBJECTS) $(TESTHARNESS)
 write_controller_test: db/write_controller_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
+merge_helper_test: db/merge_helper_test.o $(LIBOBJECTS) $(TESTHARNESS)
+	$(AM_LINK)
+
 merge_test: db/merge_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 

db/merge_helper.cc

@@ -110,15 +110,18 @@ void MergeHelper::MergeUntil(Iterator* iter, SequenceNumber stop_before,
 
     // At this point we are guaranteed that we need to process this key.
 
-    if (kTypeDeletion == ikey.type) {
-      // hit a delete
-      //   => merge nullptr with operands_
+    assert(ikey.type <= kValueTypeForSeek);
+    if (ikey.type != kTypeMerge) {
+      // hit a put/delete
+      //   => merge the put value or a nullptr with operands_
       //   => store result in operands_.back() (and update keys_.back())
       //   => change the entry type to kTypeValue for keys_.back()
-      // We are done! Return a success if the merge passes.
-
+      // We are done! Success!
+      const Slice val = iter->value();
+      const Slice* val_ptr = (kTypeValue == ikey.type) ? &val : nullptr;
       std::string merge_result;
-      Status s = TimedFullMerge(ikey.user_key, nullptr, operands_,
+      Status s =
+          TimedFullMerge(ikey.user_key, val_ptr, operands_,
                          user_merge_operator_, stats, env_, logger_,
                          &merge_result);
 
@@ -130,36 +133,7 @@ void MergeHelper::MergeUntil(Iterator* iter, SequenceNumber stop_before,
         orig_ikey.type = kTypeValue;
         UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
         operands_.back() = std::move(merge_result);
-      }
-
-      // move iter to the next entry (before doing anything else)
-      iter->Next();
-      if (steps) {
-        ++(*steps);
-      }
-      return;
-    }
-
-    if (kTypeValue == ikey.type) {
-      // hit a put
-      //   => merge the put value with operands_
-      //   => store result in operands_.back() (and update keys_.back())
-      //   => change the entry type to kTypeValue for keys_.back()
-      // We are done! Success!
-      const Slice val = iter->value();
-      std::string merge_result;
-      Status s =
-          TimedFullMerge(ikey.user_key, &val, operands_, user_merge_operator_,
-                         stats, env_, logger_, &merge_result);
-
-      // We store the result in keys_.back() and operands_.back()
-      // if nothing went wrong (i.e.: no operand corruption on disk)
-      if (s.ok()) {
-        std::string& original_key =
-            keys_.back();  // The original key encountered
-        orig_ikey.type = kTypeValue;
-        UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
-        operands_.back() = std::move(merge_result);
+        success_ = true;
       }
 
       // move iter to the next entry
@@ -168,9 +142,7 @@ void MergeHelper::MergeUntil(Iterator* iter, SequenceNumber stop_before,
         ++(*steps);
       }
       return;
-    }
-
-    if (kTypeMerge == ikey.type) {
+    } else {
       // hit a merge
       //   => merge the operand into the front of the operands_ list
       //   => use the user's associative merge function to determine how.

db/merge_helper_test.cc

@@ -0,0 +1,155 @@
+//  Copyright (c) 2013, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+
+#include <algorithm>
+#include <string>
+#include <vector>
+
+#include "db/merge_helper.h"
+#include "rocksdb/comparator.h"
+#include "util/coding.h"
+#include "util/testharness.h"
+#include "util/testutil.h"
+#include "utilities/merge_operators.h"
+
+namespace rocksdb {
+
+class MergeHelperTest : public testing::Test {
+ public:
+  MergeHelperTest() : steps_(0) {}
+  ~MergeHelperTest() = default;
+
+  void RunUInt64MergeHelper(SequenceNumber stop_before, bool at_bottom) {
+    InitIterator();
+    merge_op_ = MergeOperators::CreateUInt64AddOperator();
+    merge_helper_.reset(new MergeHelper(BytewiseComparator(), merge_op_.get(),
+          nullptr, 2U, true));
+    merge_helper_->MergeUntil(iter_.get(), stop_before, at_bottom, nullptr,
+                              &steps_, Env::Default());
+  }
+
+  void RunStringAppendMergeHelper(SequenceNumber stop_before, bool at_bottom) {
+    InitIterator();
+    merge_op_ = MergeOperators::CreateStringAppendTESTOperator();
+    merge_helper_.reset(new MergeHelper(BytewiseComparator(), merge_op_.get(),
+          nullptr, 2U, true));
+    merge_helper_->MergeUntil(iter_.get(), stop_before, at_bottom, nullptr,
+                              &steps_, Env::Default());
+  }
+
+  std::string Key(const std::string& user_key, const SequenceNumber& seq,
+      const ValueType& t) {
+    std::string ikey;
+    AppendInternalKey(&ikey, ParsedInternalKey(Slice(user_key), seq, t));
+    return ikey;
+  }
+
+  void AddKeyVal(const std::string& user_key, const SequenceNumber& seq,
+      const ValueType& t, const std::string& val) {
+    ks_.push_back(Key(user_key, seq, t));
+    vs_.push_back(val);
+  }
+
+  void InitIterator() {
+    iter_.reset(new test::VectorIterator(ks_, vs_));
+    iter_->SeekToFirst();
+  }
+
+  std::string EncodeInt(uint64_t x) {
+    std::string result;
+    PutFixed64(&result, x);
+    return result;
+  }
+
+  void CheckState(bool success, int steps, int iter_pos) {
+    ASSERT_EQ(success, merge_helper_->IsSuccess());
+    ASSERT_EQ(steps, steps_);
+    if (iter_pos == -1) {
+      ASSERT_FALSE(iter_->Valid());
+    } else {
+      ASSERT_EQ(ks_[iter_pos], iter_->key());
+    }
+  }
+
+  std::unique_ptr<test::VectorIterator> iter_;
+  std::shared_ptr<MergeOperator> merge_op_;
+  std::unique_ptr<MergeHelper> merge_helper_;
+  std::vector<std::string> ks_;
+  std::vector<std::string> vs_;
+  int steps_;
+};
+
+// If MergeHelper encounters a new key on the last level, we know that
+// the key has no more history and it can merge keys.
+TEST_F(MergeHelperTest, MergeAtBottomSuccess) {
+  AddKeyVal("a", 20, kTypeMerge, EncodeInt(1U));
+  AddKeyVal("a", 10, kTypeMerge, EncodeInt(3U));
+  AddKeyVal("b", 10, kTypeMerge, EncodeInt(4U));  // <- Iterator after merge
+
+  RunUInt64MergeHelper(0, true);
+  CheckState(true, 2, 2);
+  ASSERT_EQ(Key("a", 20, kTypeValue), merge_helper_->key());
+  ASSERT_EQ(EncodeInt(4U), merge_helper_->value());
+}
+
+// Merging with a value results in a successful merge.
+TEST_F(MergeHelperTest, MergeValue) {
+  AddKeyVal("a", 40, kTypeMerge, EncodeInt(1U));
+  AddKeyVal("a", 30, kTypeMerge, EncodeInt(3U));
+  AddKeyVal("a", 20, kTypeValue, EncodeInt(4U));  // <- Iterator after merge
+  AddKeyVal("a", 10, kTypeMerge, EncodeInt(1U));
+
+  RunUInt64MergeHelper(0, false);
+  CheckState(true, 3, 3);
+  ASSERT_EQ(Key("a", 40, kTypeValue), merge_helper_->key());
+  ASSERT_EQ(EncodeInt(8U), merge_helper_->value());
+}
+
+// Merging stops before a snapshot.
+TEST_F(MergeHelperTest, SnapshotBeforeValue) {
+  AddKeyVal("a", 50, kTypeMerge, EncodeInt(1U));
+  AddKeyVal("a", 40, kTypeMerge, EncodeInt(3U));  // <- Iterator after merge
+  AddKeyVal("a", 30, kTypeMerge, EncodeInt(1U));
+  AddKeyVal("a", 20, kTypeValue, EncodeInt(4U));
+  AddKeyVal("a", 10, kTypeMerge, EncodeInt(1U));
+
+  RunUInt64MergeHelper(31, true);
+  CheckState(false, 2, 2);
+  ASSERT_EQ(Key("a", 50, kTypeMerge), merge_helper_->keys()[0]);
+  ASSERT_EQ(EncodeInt(4U), merge_helper_->values()[0]);
+}
+
+// MergeHelper preserves the operand stack for merge operators that
+// cannot do a partial merge.
+TEST_F(MergeHelperTest, NoPartialMerge) {
+  AddKeyVal("a", 50, kTypeMerge, "v2");
+  AddKeyVal("a", 40, kTypeMerge, "v");  // <- Iterator after merge
+  AddKeyVal("a", 30, kTypeMerge, "v");
+
+  RunStringAppendMergeHelper(31, true);
+  CheckState(false, 2, 2);
+  ASSERT_EQ(Key("a", 40, kTypeMerge), merge_helper_->keys()[0]);
+  ASSERT_EQ("v", merge_helper_->values()[0]);
+  ASSERT_EQ(Key("a", 50, kTypeMerge), merge_helper_->keys()[1]);
+  ASSERT_EQ("v2", merge_helper_->values()[1]);
+}
+
+// Merging with a deletion turns the deletion into a value
+TEST_F(MergeHelperTest, MergeDeletion) {
+  AddKeyVal("a", 30, kTypeMerge, EncodeInt(3U));
+  AddKeyVal("a", 20, kTypeDeletion, "");
+
+  RunUInt64MergeHelper(15, false);
+  CheckState(true, 2, -1);
+  ASSERT_EQ(Key("a", 30, kTypeValue), merge_helper_->key());
+  ASSERT_EQ(EncodeInt(3U), merge_helper_->value());
+}
+
+}  // namespace rocksdb
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

table/merger_test.cc

@@ -5,45 +5,13 @@
 
 #include <vector>
 #include <string>
-#include <algorithm>
 
-#include "rocksdb/iterator.h"
 #include "table/merger.h"
 #include "util/testharness.h"
 #include "util/testutil.h"
 
 namespace rocksdb {
 
-class VectorIterator : public Iterator {
- public:
-  explicit VectorIterator(const std::vector<std::string>& keys)
-      : keys_(keys), current_(keys.size()) {
-    std::sort(keys_.begin(), keys_.end());
-  }
-
-  virtual bool Valid() const override { return current_ < keys_.size(); }
-
-  virtual void SeekToFirst() override { current_ = 0; }
-  virtual void SeekToLast() override { current_ = keys_.size() - 1; }
-
-  virtual void Seek(const Slice& target) override {
-    current_ = std::lower_bound(keys_.begin(), keys_.end(), target.ToString()) -
-               keys_.begin();
-  }
-
-  virtual void Next() override { current_++; }
-  virtual void Prev() override { current_--; }
-
-  virtual Slice key() const override { return Slice(keys_[current_]); }
-  virtual Slice value() const override { return Slice(); }
-
-  virtual Status status() const override { return Status::OK(); }
-
- private:
-  std::vector<std::string> keys_;
-  size_t current_;
-};
-
 class MergerTest : public testing::Test {
  public:
   MergerTest()
@@ -123,14 +91,14 @@ class MergerTest : public testing::Test {
     std::vector<Iterator*> small_iterators;
     for (size_t i = 0; i < num_iterators; ++i) {
       auto strings = GenerateStrings(strings_per_iterator, letters_per_string);
-      small_iterators.push_back(new VectorIterator(strings));
+      small_iterators.push_back(new test::VectorIterator(strings));
       all_keys_.insert(all_keys_.end(), strings.begin(), strings.end());
     }
 
     merging_iterator_.reset(
         NewMergingIterator(BytewiseComparator(), &small_iterators[0],
                            static_cast<int>(small_iterators.size())));
-    single_iterator_.reset(new VectorIterator(all_keys_));
+    single_iterator_.reset(new test::VectorIterator(all_keys_));
   }
 
   Random rnd_;

util/testutil.h

@@ -8,9 +8,13 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #pragma once
+#include <algorithm>
 #include <string>
+#include <vector>
+
 #include "db/dbformat.h"
 #include "rocksdb/env.h"
+#include "rocksdb/iterator.h"
 #include "rocksdb/slice.h"
 #include "util/random.h"
 
@@ -117,5 +121,44 @@ class SimpleSuffixReverseComparator : public Comparator {
 // endian machines.
 extern const Comparator* Uint64Comparator();
 
+// Iterator over a vector of keys/values
+class VectorIterator : public Iterator {
+ public:
+  explicit VectorIterator(const std::vector<std::string>& keys)
+      : keys_(keys), current_(keys.size()) {
+    std::sort(keys_.begin(), keys_.end());
+    values_.resize(keys.size());
+  }
+
+  VectorIterator(const std::vector<std::string>& keys,
+      const std::vector<std::string>& values)
+    : keys_(keys), values_(values), current_(keys.size()) {
+    assert(keys_.size() == values_.size());
+  }
+
+  virtual bool Valid() const override { return current_ < keys_.size(); }
+
+  virtual void SeekToFirst() override { current_ = 0; }
+  virtual void SeekToLast() override { current_ = keys_.size() - 1; }
+
+  virtual void Seek(const Slice& target) override {
+    current_ = std::lower_bound(keys_.begin(), keys_.end(), target.ToString()) -
+               keys_.begin();
+  }
+
+  virtual void Next() override { current_++; }
+  virtual void Prev() override { current_--; }
+
+  virtual Slice key() const override { return Slice(keys_[current_]); }
+  virtual Slice value() const override { return Slice(values_[current_]); }
+
+  virtual Status status() const override { return Status::OK(); }
+
+ private:
+  std::vector<std::string> keys_;
+  std::vector<std::string> values_;
+  size_t current_;
+};
+
 }  // namespace test
 }  // namespace rocksdb

utilities/merge_operators/uint64add.cc

@@ -4,6 +4,7 @@
 // of patent rights can be found in the PATENTS file in the same directory.
 
 #include <memory>
+
 #include "rocksdb/env.h"
 #include "rocksdb/merge_operator.h"
 #include "rocksdb/slice.h"