WritePrepared Txn: fix a bug in publishing recoverable state seq

Summary:
When using two_write_queue, the published seq and the last allocated sequence could be ahead of the LastSequence, even if both write queues are stopped as in WriteRecoverableState. The patch fixes a bug in WriteRecoverableState in which LastSequence was used as a reference but the result was applied to last fetched sequence and last published seq.
Closes https://github.com/facebook/rocksdb/pull/3665

Differential Revision: D7446099

Pulled By: maysamyabandeh

fbshipit-source-id: 1449bed9aed8e9db6af85946efd347cb8efd3c0b

db/db_impl_write.cc

@@ -965,7 +965,12 @@ Status DBImpl::WriteRecoverableState() {
     if (two_write_queues_) {
       log_write_mutex_.Lock();
     }
-    SequenceNumber seq = versions_->LastSequence();
+    SequenceNumber seq;
+    if (two_write_queues_) {
+      seq = versions_->FetchAddLastAllocatedSequence(0);
+    } else {
+      seq = versions_->LastSequence();
+    }
     WriteBatchInternal::SetSequence(&cached_recoverable_state_, seq + 1);
     auto status = WriteBatchInternal::InsertInto(
         &cached_recoverable_state_, column_family_memtables_.get(),
@@ -975,9 +980,9 @@ Status DBImpl::WriteRecoverableState() {
     auto last_seq = next_seq - 1;
     if (two_write_queues_) {
       versions_->FetchAddLastAllocatedSequence(last_seq - seq);
+      versions_->SetLastPublishedSequence(last_seq);
     }
     versions_->SetLastSequence(last_seq);
-    versions_->SetLastPublishedSequence(last_seq);
     if (two_write_queues_) {
       log_write_mutex_.Unlock();
     }