martinmr commented :
I looked into this. Our plan was do something similar to what Caffeine is doing to get immediate writes. Caffeine uses a small LRU whose items are either accepted or rejected into the main LRU with the use of the TinyLFU policy.
However, for this to work correctly, the write and read buffers should be lossless. This is not the case currently because we are using sync.Pool to take advantage of its internal thread-local storage. So this feature has been de-prioritized until we find an optimal way to go about this.
Most of the limitations are due to the lack of some of the features that Caffeine uses in golang.