Make recently inserted/updated records available in the buffer/cache

I am looking for tuning my PG setup such that recently inserted or updated record will be available in the buffer/cache (I believe they are same in this context). Does PostgreSQL do it by default? If yes, just increasing buffer size sufficient? What will be its effect on LRU performance -- I guess there won't be any adverse effect?

My use case is that I am going to use it as a queue and performance will be dependent upon whether the recently updated record is available in the cache.