Question

I have a Java servlet which queries a DB and shows table in the browser. I have implemented pagination so that when the user scroll the table the new request are made only then. The problem is if the user chooses to sort the table in UI based on some column, the request takes a long time because actual table in DB is quite big and it sorts the entire table and then send the sorted paged data to the client/browser. So suppose if the table has 100k rows and I have a page size of 100 rows, so is there a way to tweak the sorting in DB or in pagination in servlet that the sorting the entire 100k rows is not required.

Answer 1

Pagination may help. So, here is how it usually done. Unlike, the old paginated page by page loading web pages, when you have single page scroll. You usually have a drop down which lists the sorting column.

You first load the first page, as soon as the page’s bottom appear, you request next-page’s query via AJAX. Until here, I guess you are fine.

What seems to be troubling you that if the user has scrolled, 10 pages deep and then he sorts, you will have to load 10 pages of data in one go. This is wrong.

Two things,

1. When you change sorting criteria, you changed the context which you were viewing the table in.
2. Assume, if you load 10 pages and keep the user at 10th page. He will be surprised what happened.

So, as soon as user changed the sort criteria, you clean the DIV and load page 1, by new criteria. You see you do not have burden now. Do you?

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Couple of quick-tips:

1. I personally think it’s better to leave DBMS to do the sorting and pagination. I think it’s made to do that. You should write optimized queries.

2. Indexing columns to be sorted-by helps some.

3. If items do not change frequently, you may want to cache the pages (results from DB) with an appropriate TTL.

4. Leverage DBMS provided special functions to optimize the query. Here is an article for MySQL