WritePrepared Txn: Add MultiGet to DB

Summary:
This patch implements MultiGet API for WritePreparedTxnDB and update the existing unit tests.
Closes https://github.com/facebook/rocksdb/pull/3196

Differential Revision: D6401493

Pulled By: maysamyabandeh

fbshipit-source-id: 51501a1e32645fc2da8680e77a50035f6530f2cc

utilities/transactions/write_prepared_transaction_test.cc

@@ -305,6 +305,20 @@ class WritePreparedTransactionTest : public TransactionTest {
       } else {
         ASSERT_EQ(kv.second, "NOT_FOUND");
       }
+
+      // Try with MultiGet API too
+      std::vector<std::string> values;
+      auto s_vec = db->MultiGet(read_options, {db->DefaultColumnFamily()},
+                                {kv.first}, &values);
+      ASSERT_EQ(1, values.size());
+      ASSERT_EQ(1, s_vec.size());
+      s = s_vec[0];
+      ASSERT_TRUE(s.ok() || s.IsNotFound());
+      if (s.ok()) {
+        ASSERT_TRUE(kv.second == values[0]);
+      } else {
+        ASSERT_EQ(kv.second, "NOT_FOUND");
+      }
     }
   }
 
@@ -1081,6 +1095,19 @@ void ASSERT_SAME(TransactionDB* db, Status exp_s, PinnableSlice& exp_v,
   if (s.ok()) {
     ASSERT_TRUE(exp_v == v);
   }
+
+  // Try with MultiGet API too
+  std::vector<std::string> values;
+  auto s_vec =
+      db->MultiGet(roptions, {db->DefaultColumnFamily()}, {key}, &values);
+  ASSERT_EQ(1, values.size());
+  ASSERT_EQ(1, s_vec.size());
+  s = s_vec[0];
+  ASSERT_TRUE(exp_s == s);
+  ASSERT_TRUE(s.ok() || s.IsNotFound());
+  if (s.ok()) {
+    ASSERT_TRUE(exp_v == values[0]);
+  }
 }
 
 TEST_P(WritePreparedTransactionTest, RollbackTest) {

utilities/transactions/write_prepared_txn_db.cc

@@ -75,6 +75,22 @@ Status WritePreparedTxnDB::Get(const ReadOptions& options,
                            &callback);
 }
 
+std::vector<Status> WritePreparedTxnDB::MultiGet(
+    const ReadOptions& options,
+    const std::vector<ColumnFamilyHandle*>& column_family,
+    const std::vector<Slice>& keys, std::vector<std::string>* values) {
+  assert(values);
+  size_t num_keys = keys.size();
+  values->resize(num_keys);
+
+  std::vector<Status> stat_list(num_keys);
+  for (size_t i = 0; i < num_keys; ++i) {
+    std::string* value = values ? &(*values)[i] : nullptr;
+    stat_list[i] = this->Get(options, column_family[i], keys[i], value);
+  }
+  return stat_list;
+}
+
 // Struct to hold ownership of snapshot and read callback for iterator cleanup.
 struct WritePreparedTxnDB::IteratorState {
   IteratorState(WritePreparedTxnDB* txn_db, SequenceNumber sequence,

utilities/transactions/write_prepared_txn_db.h

@@ -72,6 +72,13 @@ class WritePreparedTxnDB : public PessimisticTransactionDB {
                      ColumnFamilyHandle* column_family, const Slice& key,
                      PinnableSlice* value) override;
 
+  using DB::MultiGet;
+  virtual std::vector<Status> MultiGet(
+      const ReadOptions& options,
+      const std::vector<ColumnFamilyHandle*>& column_family,
+      const std::vector<Slice>& keys,
+      std::vector<std::string>* values) override;
+
   using DB::NewIterator;
   virtual Iterator* NewIterator(const ReadOptions& options,
                                 ColumnFamilyHandle* column_family) override;