Maybe I am misunderstanding but the postgres buffer cache is LRU and will evict pages right? At times data may go to disk and then during serving it will have t

Maybe I am misunderstanding but the postgres buffer cache is LRU and will evict pages right? At times data may go to disk and then during serving it will have to be loaded into memory? So it is quite dependent on the size of your buffer cache as well as contention for that buffer cache. Also the cache access patterns will vary between these implementations and is worth considering.