Support dependency barriers.

diff --git a/src/include/storage/barrier.h b/src/include/storage/barrier.h
index cd85633c138f4da7b7ea3698a171f935c5d2f3da..dbcc0f8a6420d5db86957514090e4416055163a5 100644 (file)
--- a/src/include/storage/barrier.h
+++ b/src/include/storage/barrier.h
@@ -20,4 +20,12 @@
  */
 #include "port/atomics.h"
 
+/*
+ * If dependency barriers are undefined, we define them as a no-op.  The only
+ * known platform where anything more is required is DEC Alpha.
+ */
+#if !defined(pg_read_barrier_depends)
+#define pg_read_barrier_depends()
+#endif
+
 #endif   /* BARRIER_H */