在网页中使用分页是否真的对性能有任何好处？

Question

I'm programming a website in Java using struts as framework, and I tried to use pagination to break a query who could take too long to return, using a query similar to this:

select col
from   ( select col,rownum AS rn from table )
where  rn >= 1
and    rn <=10

That is from what I've seen the stardard way for doing pagination, but I don't see any performance improvement over just select the entire table and paginate in Java only, as for Oracle to calculate the rownum , it has to execute my query once.

Ideally I want to only search for a subset of this table results, instead of searching the whole table and then discarding part of the results. Is there a way for doing that? Because if not, I can't see why lazy pagination would be better then just load the whole list and then separate in Java.

Answer 1

There is, but you won't see it until you have enough data to simulate a fully grown database.

As others mentioned in the comments, generate a few million rows into your table, and then start using pagination and watch the plan of your query. Now you have something that has the smell of real-life, that you can compare to caching the table in memory.