pgpool_lb_algorithm.c

/*
 * Select load balancing node
 */
int select_load_balancing_node(void)
{
	int selected_slot;
	double total_weight,r;
	int i;

	/* choose a backend in random manner with weight */
	selected_slot = MASTER_NODE_ID;
	total_weight = 0.0;

	for (i=0;i<NUM_BACKENDS;i++)
	{
		if (VALID_BACKEND(i))
		{
			total_weight += BACKEND_INFO(i).backend_weight;
		}
	}

#if defined(sun) || defined(__sun)
	r = (((double)rand())/RAND_MAX) * total_weight;
#else
	r = (((double)random())/RAND_MAX) * total_weight;
#endif

	total_weight = 0.0;
	for (i=0;i<NUM_BACKENDS;i++)
	{
		if (VALID_BACKEND(i) && BACKEND_INFO(i).backend_weight > 0.0)
		{
			if(r >= total_weight)
				selected_slot = i;
			else
				break;
			total_weight += BACKEND_INFO(i).backend_weight;
		}
	}

	pool_debug("select_load_balancing_node: selected backend id is %d", selected_slot);
	return selected_slot;
}