Question

I would like to develop a Forum from scratch, with special needs and customization.

I would like to prepare my forum for intensive usage and wondering how to cache things like User posts count and User replies count.

Having only three tables, tblForum, tblForumTopics, tblForumReplies, what is the best approach of cache the User topics and replies counts ?

Think at a simple scenario: user press a link and open the Replies.aspx?id=x&page=y page, and start reading replies. On the HTTP Request, the server will run an SQL command wich will fetch all replies for that page, also “inner joining with tblForumReplies to find out the number of User replies for each user that replied.”

select 
    tblForumReplies.*,
    tblFR.TotalReplies
from 
   tblForumReplies
   inner join 
     (
       select IdRepliedBy, count(*) as TotalReplies
       from tblForumReplies
       group by IdRepliedBy
     ) as tblFR 
     on tblFR.IdRepliedBy = tblForumReplies.IdRepliedBy

Unfortunately this approach is very cpu intensive, and I would like to see your ideas of how to cache things like table Counts.

If counting replies for each user on insert/delete, and store it in a separate field, how to syncronize with manual data changing. Suppose I will manually delete Replies from SQL.

Answer 1

These are the three approaches I’d be thinking of:

1) Maybe SQL Server performance will be good enough that you don’t need to cache. You might be underestimating how well SQL Server can do its job. If you do your joins right, it’s just one query to get all the counts of all the users that are in that thread. If you are thinking of this as one query per user, that’s wrong.

2) Don’t cache. Redundantly store the user counts on the user table. Update the user row whenever a post is inserted or deleted.

3) If you have thousands of users, even many thousand, but not millions, you might find that it’s practical to cache user and their counts in the web layer’s memory – for ASP.NET, the “Application” cache.