synchronize the mmap sizes between processes

src/runtime/c/pgf/db.h

@@ -61,6 +61,7 @@ private:
     int fd;
     const char *filepath;
     malloc_state* ms;
+    size_t mmap_size;
 
 #ifndef _WIN32
     pthread_rwlock_t *rwlock;
@@ -117,6 +118,8 @@ private:
     PGF_INTERNAL_DECL void lock(DB_scope_mode m);
     PGF_INTERNAL_DECL void unlock();
 
+    PGF_INTERNAL_DECL void resize_map(size_t new_size);
+
     friend class DB_scope;
 };