Better support for merge operation with data block hash index (#11356)

Summary:
when data block hash index finds a key of op_type `kTypeMerge`, do not redo data block seek.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11356

Test Plan:
- added new unit test
- crash test: `python3 tools/db_crashtest.py whitebox --simple --use_merge=1 --data_block_index_type=1`
- benchmark see slight improvement in read throughput:
```
TEST_TMPDIR=/dev/shm/hashindex ./db_bench -benchmarks=mergerandom -use_existing_db=false -num=10000000 -compression_type=none -level_compaction_dynamic_level_bytes=1 -merge_operator=PutOperator -write_buffer_size=1000000 --use_data_block_hash_index=1

TEST_TMPDIR=/dev/shm/hashindex ./db_bench -benchmarks=readrandom[-X10] -use_existing_db=true -num=10000000 -merge_operator=PutOperator -readonly=1 -disable_auto_compactions=1 -reads=100000

Main: readrandom [AVG 10 runs] : 29526 (± 1118) ops/sec;    2.1 (± 0.1) MB/sec
Post-PR: readrandom [AVG 10 runs] : 31095 (± 662) ops/sec;    2.2 (± 0.0) MB/sec
```

Reviewed By: pdillinger

Differential Revision: D44759895

Pulled By: cbi42

fbshipit-source-id: 387f0c35938c7e0e96b810ca3babf1967fc68191

db/db_merge_operator_test.cc

@@ -358,6 +358,48 @@ TEST_F(DBMergeOperatorTest, MergeOperatorFailsWithMustMerge) {
   }
 }
 
+TEST_F(DBMergeOperatorTest, DataBlockBinaryAndHash) {
+  // Basic test to check that merge operator works with data block index type
+  // DataBlockBinaryAndHash.
+  Options options;
+  options.create_if_missing = true;
+  options.merge_operator.reset(new TestPutOperator());
+  options.env = env_;
+  BlockBasedTableOptions table_options;
+  table_options.block_restart_interval = 16;
+  table_options.data_block_index_type =
+      BlockBasedTableOptions::DataBlockIndexType::kDataBlockBinaryAndHash;
+  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
+  DestroyAndReopen(options);
+
+  const int kNumKeys = 100;
+  for (int i = 0; i < kNumKeys; ++i) {
+    ASSERT_OK(db_->Merge(WriteOptions(), Key(i), std::to_string(i)));
+  }
+  ASSERT_OK(Flush());
+  std::string value;
+  for (int i = 0; i < kNumKeys; ++i) {
+    ASSERT_OK(db_->Get(ReadOptions(), Key(i), &value));
+    ASSERT_EQ(std::to_string(i), value);
+  }
+
+  std::vector<const Snapshot*> snapshots;
+  for (int i = 0; i < kNumKeys; ++i) {
+    ASSERT_OK(db_->Delete(WriteOptions(), Key(i)));
+    for (int j = 0; j < 3; ++j) {
+      ASSERT_OK(db_->Merge(WriteOptions(), Key(i), std::to_string(i * 3 + j)));
+      snapshots.push_back(db_->GetSnapshot());
+    }
+  }
+  ASSERT_OK(Flush());
+  for (int i = 0; i < kNumKeys; ++i) {
+    ASSERT_OK(db_->Get(ReadOptions(), Key(i), &value));
+    ASSERT_EQ(std::to_string(i * 3 + 2), value);
+  }
+  for (auto snapshot : snapshots) {
+    db_->ReleaseSnapshot(snapshot);
+  }
+}
 
 class MergeOperatorPinningTest : public DBMergeOperatorTest,
                                  public testing::WithParamInterface<bool> {

table/block_based/block.cc

@@ -307,11 +307,11 @@ void MetaBlockIter::SeekImpl(const Slice& target) {
 // target = "seek_user_key @ type | seqno".
 //
 // For any type other than kTypeValue, kTypeDeletion, kTypeSingleDeletion,
-// kTypeBlobIndex, or kTypeWideColumnEntity, this function behaves identically
-// to Seek().
+// kTypeBlobIndex, kTypeWideColumnEntity or kTypeMerge, this function behaves
+// identically to Seek().
 //
 // For any type in kTypeValue, kTypeDeletion, kTypeSingleDeletion,
-// kTypeBlobIndex, or kTypeWideColumnEntity:
+// kTypeBlobIndex, kTypeWideColumnEntity, or kTypeMerge:
 //
 // If the return value is FALSE, iter location is undefined, and it means:
 // 1) there is no key in this block falling into the range:
@@ -412,11 +412,11 @@ bool DataBlockIter::SeekForGetImpl(const Slice& target) {
   ValueType value_type = ExtractValueType(raw_key_.GetInternalKey());
   if (value_type != ValueType::kTypeValue &&
       value_type != ValueType::kTypeDeletion &&
+      value_type != ValueType::kTypeMerge &&
       value_type != ValueType::kTypeSingleDeletion &&
       value_type != ValueType::kTypeBlobIndex &&
       value_type != ValueType::kTypeWideColumnEntity) {
     SeekImpl(target);
-    return true;
   }
 
   // Result found, and the iter is correctly set.