Fix BlobDB::Get which only get out the value offset

Summary:
Blob db use StackableDB::get which only get out the
value offset, but not the value.
Fix by making BlobDB::Get override the designated getter.
Closes https://github.com/facebook/rocksdb/pull/2553

Differential Revision: D5396823

Pulled By: yiwu-arbug

fbshipit-source-id: 5a7d1cf77ee44490f836a6537225955382296878

utilities/blob_db/blob_db.h

@@ -134,7 +134,7 @@ class BlobDB : public StackableDB {
   using rocksdb::StackableDB::Get;
   virtual Status Get(const ReadOptions& options,
                      ColumnFamilyHandle* column_family, const Slice& key,
-                     std::string* value) override = 0;
+                     PinnableSlice* value) override = 0;
 
   using rocksdb::StackableDB::MultiGet;
   virtual std::vector<Status> MultiGet(

utilities/blob_db/blob_db_impl.cc

@@ -1326,7 +1326,7 @@ Status BlobDBImpl::CommonGet(const ColumnFamilyData* cfd, const Slice& key,
 
 Status BlobDBImpl::Get(const ReadOptions& options,
                        ColumnFamilyHandle* column_family, const Slice& key,
-                       std::string* value) {
+                       PinnableSlice* value) {
   auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
   auto cfd = cfh->cfd();
 
@@ -1341,7 +1341,8 @@ Status BlobDBImpl::Get(const ReadOptions& options,
     return s;
   }
 
-  s = CommonGet(cfd, key, index_entry, value);
+  s = CommonGet(cfd, key, index_entry, value->GetSelf());
+  value->PinSelf();
   return s;
 }
 

utilities/blob_db/blob_db_impl.h

@@ -162,7 +162,7 @@ class BlobDBImpl : public BlobDB {
 
   using rocksdb::StackableDB::Get;
   Status Get(const ReadOptions& options, ColumnFamilyHandle* column_family,
-             const Slice& key, std::string* value) override;
+             const Slice& key, PinnableSlice* value) override;
 
   using rocksdb::StackableDB::NewIterator;
   virtual Iterator* NewIterator(const ReadOptions& opts,

utilities/blob_db/blob_db_test.cc

@@ -130,6 +130,28 @@ TEST_F(BlobDBTest, Put) {
   VerifyDB(data);
 }
 
+TEST_F(BlobDBTest, StackableDBGet) {
+  Random rnd(301);
+  BlobDBOptionsImpl bdb_options;
+  bdb_options.disable_background_tasks = true;
+  Open(bdb_options);
+  std::map<std::string, std::string> data;
+  for (size_t i = 0; i < 100; i++) {
+    PutRandom("key" + ToString(i), &rnd, &data);
+  }
+  for (size_t i = 0; i < 100; i++) {
+    StackableDB *db = blob_db_;
+    ColumnFamilyHandle *column_family = db->DefaultColumnFamily();
+    std::string key = "key" + ToString(i);
+    PinnableSlice pinnable_value;
+    ASSERT_OK(db->Get(ReadOptions(), column_family, key, &pinnable_value));
+    std::string string_value;
+    ASSERT_OK(db->Get(ReadOptions(), column_family, key, &string_value));
+    ASSERT_EQ(string_value, pinnable_value.ToString());
+    ASSERT_EQ(string_value, data[key]);
+  }
+}
+
 TEST_F(BlobDBTest, WriteBatch) {
   Random rnd(301);
   BlobDBOptionsImpl bdb_options;