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

Hi,

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.

Thank you.

regards
Sachin