Add GetSharedSnapshot() to Transaction

include/rocksdb/utilities/transaction.h

@@ -193,6 +193,10 @@ class Transaction {
   // is called, or the Transaction is deleted.
   virtual const Snapshot* GetSnapshot() const = 0;
 
+  // Returns the Snapshot created by the last call to SetSnapshot().
+  // The returned snapshot can outlive the transaction.
+  virtual std::shared_ptr<const Snapshot> GetSharedSnapshot() const = 0;
+
   // Clears the current snapshot (i.e. no snapshot will be 'set')
   //
   // This removes any snapshot that currently exists or is set to be created

utilities/transactions/transaction_base.h

@@ -206,6 +206,10 @@ class TransactionBaseImpl : public Transaction {
     return snapshot_.get();
   }
 
+  std::shared_ptr<const Snapshot> GetSharedSnapshot() const override {
+    return snapshot_;
+  }
+
   virtual void SetSnapshot() override;
   void SetSnapshotOnNextOperation(
       std::shared_ptr<TransactionNotifier> notifier = nullptr) override;