Reduce GC pause time

On my test instance, I'm using a 3h retention and feeding in about 2500 records / s. Each record has a 10-byte key and a random 1000-byte value.

I have about ~27GB of data and I'm seeing a 2-5GB heap (it fluctuates). GC pause times eventually stabilize at about 3s.

I want to reduce this by at least 10x. The main technique will be to purge pointers from the primary heap maps.