Parallel reading is effectively random order, not sequential

geojson.c

@@ -1033,7 +1033,7 @@ void *run_read_parallel(void *v) {
 		perror("map intermediate input");
 		exit(EXIT_FAILURE);
 	}
-	madvise(map, a->len, MADV_SEQUENTIAL);
+	madvise(map, a->len, MADV_RANDOM);  // sequential, but from several pointers at once
 
 	do_read_parallel(map, a->len, a->offset, a->reading, a->reader, a->progress_seq, a->exclude, a->include, a->exclude_all, a->fname, a->basezoom, a->source, a->nlayers, a->droprate, a->initialized, a->initial_x, a->initial_y);