Is caching a good idea? If so, where?

Question

I have an asp.net web site with 10-25k visitors a day (peaks of over 60k before holidays). Pages/visit is also high, since it's a content site. I have a few specific pages which generate about 60% of the traffic. These pages are a bit complex and are DB heavy (sql server 2008 r2 backend). I was wondering if it's worth "caching" a static version of these pages (I hear this is possible) and only re-render them when something changes (about once in 48hs). Does this sound like a good idea? Where would be the best place to implement this? (asp.net, iis, db)

Update: Looks like a good option for me is outputcache with SqlDependency. I see a reference to some kind of SQL server notification for invalidating the cache, but I only see talk of SQL server 2005. Has this option been deprecated by Microsoft? Any new way to handle this?

Answer 1

Caching may or may not help. For example, if a site has low traffic and if the caching is enabled, the server processes to create the cache before serving the request. And because the traffic is low, there can be enough delay between successive requests. So the cached version may even expire and the server again creates a new cached version. This process makes the response even slower than normal. Read more on: http://tipscow.com/caching-the-good-the-bad/

I have myself experienced this issue.

If the traffic is good, caching may help you have better load times. Cheers Aditya

Answer 2

I don't have much experience in caching, but this is what I would try to do:

• I would look at your stats and run some profiles, see which are the most heavily visited pages that run the most expensive SQL queries. Pick one or two of the most expensive pages.

• If the page is pseudo static, that is, no data on it such as your logged in username, no comments, etc etc, you can cache the entire page. You can set a relatively long cache as well, anything from 1 min to a few hours.

• If the page has some dynamic real time content on it, such as comments, you can identify the static controls and cache those individually. Don't put a page wide cache on.

Good luck, sounds like a cache could improve performance.

Answer 3

Caching is a broad term that can happen at a number of different points. The optimum solution may be a combination of some or all.

For example, you can add page, or output caching as described here, which caches output on the web server, which I think is what you were referring to.

In addition, you can cache the data in memory using something like memcached, so that your data is more available to the web server as it builds the page, but you need to look at cache hit rate to know for sure that you are caching the right data.

Also, although slightly off the topic of improving db heavy pages, you can cache static resources that change infrequently like images, css and include files using a content delivery network. Any CDN will almost certainly have a higher bandwidth and a cheaper data plan than your own connection because of the economies of scale, so the more of your content you can serve from there the better, in general.

Your first question was "I was wondering if it's worth "caching" a static version of these pages". I guess the answer to that depends on whether there is a performance problem at the moment, and where the cause of that problem is. If the pages are being served quickly and reliably, then quite possibly it's not worth implementing caching. If there is a performance problem, then where is it? Is it in db read time, or is it in the time spent building the page once the data has been returned?