PostgreSQL caching

Hello,

I have the following problem:

When I run some query after I just run the Postmaster, it takse
several seconds to execute (sometimes more than 10), if I rerun it
again afterwards, it takes mere milliseconds.

So, I guess it has to do with PostgreSQL caching.. But how exactly
does it work? What does it cache? And how can I control it?

I would like to load selected information in the memory before a user
runs the query. Can I do it somehow? As PostgreSQL is used in my case
as webserver, it isn't really helping if the user has to wait 10
seconds every time he goes to a new page (even if refreshing the page
would be really quick, sine Postgre already loaded the data to
memory).

P.S If the query or its EXPLAIN are critical for a better
understanding, let me know.

Regards,
 Vitaly Belman

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