As discussed in Chapter 9, Aggregations, DTrace's aggregations allow for a scalable way of aggregating data. Associative arrays might appear to offer similar functionality to aggregations. However, by nature of being global, general-purpose variables, they cannot offer the linear scalability of aggregations. You should therefore prefer to use aggregations over associative arrays when possible. The following example is not recommended:

syscall:::entry
{
	totals[execname]++;
}

syscall::rexit:entry
{
	printf("%40s %d\n", execname, totals[execname]);
	totals[execname] = 0;
}

The following example is preferable:

syscall:::entry
{
	@totals[execname] = count();
}

END
{
	printa("%40s %@d\n", @totals);
}