Support SuperSnapshots in one more variant of MultiGet (#296)

This PR contains a couple of improvements to SuperSnapshots
implementation, the major one being support for one more variant of
MultiGet (there are three total, we now support two).

Author: igorcanadi

cloud/replication_test.cc

@@ -1315,13 +1315,15 @@ TEST_F(ReplicationTest, SuperSnapshot) {
   ASSERT_OK(follower->Get(ro, "k1", &val));
   EXPECT_EQ(val, "v1");
 
-  auto iter = follower->NewIterator(ro, follower->DefaultColumnFamily());
+  auto iter = std::unique_ptr<rocksdb::Iterator>(
+      follower->NewIterator(ro, follower->DefaultColumnFamily()));
   iter->SeekToFirst();
   EXPECT_TRUE(iter->Valid());
   EXPECT_EQ(iter->key(), "k1");
   EXPECT_EQ(iter->value(), "v1");
   iter->Next();
   EXPECT_FALSE(iter->Valid());
+  iter.reset();
 
   ro.snapshot = nullptr;
   ASSERT_OK(follower->Get(ro, followerCF("cf1"), "cf1k1", &val));
@@ -1339,19 +1341,33 @@ TEST_F(ReplicationTest, SuperSnapshot) {
   cfs.push_back(followerCF("cf1"));
   std::vector<std::string> vals;
 
+  // Multiget on cf1, snapshot
+  ro.snapshot = snapshots[1];
   auto statuses = follower->MultiGet(ro, cfs, keys, &vals);
   ASSERT_OK(statuses[0]);
   ASSERT_TRUE(statuses[1].IsNotFound());
   ASSERT_EQ(vals[0], "cf1v1");
 
+  // Multiget on cf1, no snapshot
   ro.snapshot = nullptr;
   statuses = follower->MultiGet(ro, cfs, keys, &vals);
   ASSERT_OK(statuses[0]);
   ASSERT_TRUE(statuses[1].IsNotFound());
   ASSERT_EQ(vals[0], "cf1v2");
 
-  // Column family <-> snapshot mismatch
+  // Multiget on default column family, snapshot, pinnable values
   ro.snapshot = snapshots[0];
+  keys[0] = "k1";
+  std::vector<PinnableSlice> pinnableValues;
+  pinnableValues.resize(2);
+  follower->MultiGet(ro, follower->DefaultColumnFamily(), 2,
+                                keys.data(), pinnableValues.data(), statuses.data(), true);
+  ASSERT_OK(statuses[0]);
+  ASSERT_TRUE(statuses[1].IsNotFound());
+  ASSERT_EQ(pinnableValues[0], "v1");
+  pinnableValues.clear();
+
+  // Column family <-> snapshot mismatch
   ASSERT_FALSE(follower->Get(ro, followerCF("cf1"), "cf1k1", &val).ok());
 
   follower->ReleaseSnapshot(snapshots[0]);

db/db_impl/db_impl.cc

@@ -3139,8 +3139,9 @@ void DBImpl::MultiGet(const ReadOptions& read_options, const size_t num_keys,
   if (dynamic_cast<const SuperSnapshotImpl*>(read_options.snapshot)) {
     for (size_t i = 0; i < num_keys; ++i) {
       statuses[i] = Status::NotSupported(
-          "MultiGet with timestamps does not support super snapshot");
+          "This variant of MultiGet does not yet support super snapshots");
     }
+    return;
   }
   // RocksDB-Cloud contribution end
 
@@ -3400,8 +3401,12 @@ void DBImpl::MultiGetWithCallback(
                           multiget_cf_data[0].super_version, consistent_seqnum,
                           read_callback);
   assert(s.ok() || s.IsTimedOut() || s.IsAborted());
-  ReturnAndCleanupSuperVersion(multiget_cf_data[0].cfd,
-                               multiget_cf_data[0].super_version);
+  // RocksDB-Cloud contribution begin
+  if (!dynamic_cast<const SuperSnapshotImpl*>(read_options.snapshot)) {
+    ReturnAndCleanupSuperVersion(multiget_cf_data[0].cfd,
+                                 multiget_cf_data[0].super_version);
+  }
+  // RocksDB-Cloud contribution end
 }
 
 // The actual implementation of batched MultiGet. Parameters -
@@ -3844,10 +3849,12 @@ Iterator* DBImpl::NewIterator(const ReadOptions& read_options,
     result = nullptr;
 
 #else
+    // RocksDB-Cloud contribution begin
     if (dynamic_cast<const SuperSnapshotImpl*>(read_options.snapshot)) {
       return NewErrorIterator(Status::NotSupported(
           "Tailing iterator not supported with super snapshot"));
     }
+    // RocksDB-Cloud contribution end
 
     SuperVersion* sv = cfd->GetReferencedSuperVersion(this);
     auto iter = new ForwardIterator(this, read_options, cfd, sv,
@@ -4077,6 +4084,8 @@ Status DBImpl::GetSuperSnapshots(
   return Status::InvalidArgument(
       "GetSuperSnapshots only supported in RocksDB compiled with USE_RTTI=1");
 #endif
+  InstrumentedMutexLock l(&mutex_);
+
   if (!is_snapshot_supported_) {
     return Status::InvalidArgument("Snapshot not supported");
   }
@@ -4092,7 +4101,8 @@ Status DBImpl::GetSuperSnapshots(
   for (auto& cf : column_families) {
     auto cfh = static_cast_with_check<ColumnFamilyHandleImpl>(cf);
     auto cfd = cfh->cfd();
-    auto sv = cfd->GetReferencedSuperVersion(this);
+    auto sv = cfd->GetSuperVersion();
+    sv->Ref();
     auto ss = new SuperSnapshotImpl(cfd, sv);
     snapshots_.New(ss, snapshot_seq, unix_time,
                    /*is_write_conflict_boundary=*/false);