Similarly to the allocation rate, the main impact of the promotion rate is the change of frequency in GC pauses. But as opposed to the allocation rate that affects the frequency of minor GC events, the promotion rate affects the frequency of major GC events. Let me explain – the more stuff you promote to the old generation the faster you will fill it up. Filling the old generation faster means that the frequency of the GC events cleaning the old generation will increase.
As we have shown in earlier chapters, full garbage collections typically require much more time, as they have to interact with many more objects, and perform additional complex activities such as defragmentation.