Add fetchBatch Backend interface

src/ripple/nodestore/Backend.h

@@ -65,6 +65,16 @@ public:
     */
     virtual Status fetch (void const* key, NodeObject::Ptr* pObject) = 0;
 
+    /** Return `true` if batch fetches are optimized. */
+    virtual
+    bool
+    canFetchBatch() = 0;
+
+    /** Fetch a batch synchronously. */
+    virtual
+    std::vector<std::shared_ptr<NodeObject>>
+    fetchBatch (std::size_t n, void const* const* keys) = 0;
+
     /** Store a single object.
         Depending on the implementation this may happen immediately
         or deferred using a scheduled task.

src/ripple/nodestore/backend/MemoryFactory.cpp

@@ -128,6 +128,19 @@ public:
         return ok;
     }
 
+    bool
+    canFetchBatch() override
+    {
+        return false;
+    }
+
+    std::vector<std::shared_ptr<NodeObject>>
+    fetchBatch (std::size_t n, void const* const* keys) override
+    {
+        throw std::runtime_error("pure virtual called");
+        return {};
+    }
+
     void
     store (NodeObject::ref object)
     {

src/ripple/nodestore/backend/NuDBFactory.cpp

@@ -148,6 +148,19 @@ public:
         return status;
     }
 
+    bool
+    canFetchBatch() override
+    {
+        return false;
+    }
+
+    std::vector<std::shared_ptr<NodeObject>>
+    fetchBatch (std::size_t n, void const* const* keys) override
+    {
+        throw std::runtime_error("pure virtual called");
+        return {};
+    }
+
     void
     do_insert (std::shared_ptr <NodeObject> const& no)
     {

src/ripple/nodestore/backend/NullFactory.cpp

@@ -53,6 +53,19 @@ public:
         return notFound;
     }
 
+    bool
+    canFetchBatch() override
+    {
+        return false;
+    }
+
+    std::vector<std::shared_ptr<NodeObject>>
+    fetchBatch (std::size_t n, void const* const* keys) override
+    {
+        throw std::runtime_error("pure virtual called");
+        return {};
+    }
+
     void
     store (NodeObject::ref object)
     {

src/ripple/nodestore/backend/RocksDBFactory.cpp

@@ -266,6 +266,19 @@ public:
         return status;
     }
 
+    bool
+    canFetchBatch() override
+    {
+        return false;
+    }
+
+    std::vector<std::shared_ptr<NodeObject>>
+    fetchBatch (std::size_t n, void const* const* keys) override
+    {
+        throw std::runtime_error("pure virtual called");
+        return {};
+    }
+
     void
     store (NodeObject::ref object)
     {

src/ripple/nodestore/backend/RocksDBQuickFactory.cpp

@@ -250,12 +250,25 @@ public:
         return status;
     }
 
+    bool
+    canFetchBatch() override
+    {
+        return false;
+    }
+
     void
     store (NodeObject::ref object)
     {
         storeBatch(Batch{object});
     }
 
+    std::vector<std::shared_ptr<NodeObject>>
+    fetchBatch (std::size_t n, void const* const* keys) override
+    {
+        throw std::runtime_error("pure virtual called");
+        return {};
+    }
+
     void
     storeBatch (Batch const& batch)
     {