Big Data with JSON and jsp and EJB

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Java

PostgreSQL

hi everybody here,
i wanna ask about a big data using postgresql and using EJB(jboss) as the remote bean, also as the webserver i'm using tomcat and pure html+jsp(JSON).

let's say in a month i'm gonna have 10000 rows of data, so if i'm query it for 1 day, it gotcha be 100 rows, and it's still fine, but after i query for 3 days or more, let's say it return between 10000 and 1000 rows, it's gonna take a long time.

how do i optimize my query to let it quicker ?

thanks.