presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/util/ConcatPageSource.java/ConcatPageSource/getSystemMemoryUsage
class ConcatPageSource:    @Override
    public long getSystemMemoryUsage()
    {
        return (current != null) ? current.getSystemMemoryUsage() : 0;
    }