bind caching algorithm?

[KyoungSoo Park]

Hi,

Is there anyone who's familar with bind's caching algorithm?
I know it's based on TTLs of the result records, but there should be an 
evicting algorthm as well.
How does bind do cache eviction? LRU, LFU ... ?
How does it search for a cached record? Is it using hashing(what kind of)?

I don't think bind is doing very stupid thing like linear search on some 
lists or even incur thrashing,
but when I do stress test with a lot of requests, usually the memory 
size gets bigger and bigger
and at some points, the reponse gets very slow. I know I can place a 
limit on the caching memory size,
but it seems not quite well controlled with that option.

Thanks,
KyoungSoo