diff --git a/fdbclient/JsonString.h b/fdbclient/JsonString.h
index 30e0ae2a3a..11d2d578ac 100755
--- a/fdbclient/JsonString.h
+++ b/fdbclient/JsonString.h
@@ -97,20 +97,33 @@ protected:
 		write(val ? "true" : "false");
 	}
 
+	template<typename T> inline void writeFormat(const char *fmt, const T &val) {
+		VString &dst = jsonText.back();
+		const int limit = 30;
+		dst.reserve(arena, dst.size() + limit);
+		int len = snprintf(dst.end(), limit, fmt, val);
+		if(len > 0 && len < limit) {
+			dst.extendUnsafeNoReallocNoInit(len);
+		}
+		else {
+			write(format(fmt, val));
+		}
+	}
+
 	void writeValue(const int64_t& val) {
-		write(format("%lld",val));
+		writeFormat("%lld", val);
 	}
 
 	void writeValue(const uint64_t& val) {
-		write(format("%llu",val));
+		writeFormat("%llu", val);
 	}
 
 	void writeValue(const int& val) {
-		write(format("%d",val));
+		writeFormat("%d", val);
 	}
 
 	void writeValue(const double& val) {
-		write(format("%g",val));
+		writeFormat("%g", val);
 	}
 
 	bool shouldEscape(char c) {
diff --git a/flow/Arena.h b/flow/Arena.h
index 29505e7e64..b776b72289 100644
--- a/flow/Arena.h
+++ b/flow/Arena.h
@@ -595,6 +595,7 @@ public:
 	}
 
 	VectorRef( T* data, int size ) : data(data), m_size(size), m_capacity(size) {}
+	VectorRef( T* data, int size, int capacity ) : data(data), m_size(size), m_capacity(capacity) {}
 	//VectorRef( const VectorRef<T>& toCopy ) : data( toCopy.data ), m_size( toCopy.m_size ), m_capacity( toCopy.m_capacity ) {}
 	//VectorRef<T>& operator=( const VectorRef<T>& );
 
@@ -690,6 +691,10 @@ public:
 		return m_capacity;
 	}
 
+	void extendUnsafeNoReallocNoInit(int amount) {
+		m_size += amount;
+	}
+
 private:
 	T* data;
 	int m_size, m_capacity;