I was simple cruising through the modx options and i noticed the option to cache snippets. I was wondering what kind of effect this would have (downsides) to my site. I know that caching would improve the loading time of the site by keeping them 'cached' after the first time and then only reloading the updates but this all seems to good to be true. My question is simple: are there any downsides to caching snippets? Cheers, Marco.
Great question!
The first rule of Modx is (almost) always cache. They've said so in their own blog.
As you said, the loading time will be lower. Let's just get the basics on the floor first. When you chose to cache a page, the page with all the output is stored as a file in your cache-folder. If you have a small and simple site, you might not see the biggest difference in caching and not, but if you have a complex one with lots of chunks-in-chunks, snippets parsing chunks etc, the difference is enormous. Some of the websites I've made goes down 15-30 levels to parse the content in come sections. Loading all this fresh from the database can take up to a coupe of seconds, while loading a flat-file would take only a few microseconds. There is a HUGE difference (remember that).
Now. You can cache both snippets and chunks. Important to remember. You can also cache one chunk while uncache the next level. Using Modx's brilliant markup, you can chose what to cache and what to uncache, but in general you want as much as possible cached.
You ask about the downside. There are none, but there are a few cases where you can't use cached snippets/chunks. As mentioned earlier, the cached response is divided into each page. That means that if you have a page (or url or whatever you want to call it), where you display different content based on for example GET-parameters. You can't cache a search-result (because the content changes) or a page with pagination (?page=1, ?page=2 etc would produce different output on the same page). Another case is when a snippet's output is random/different every time. Say you put a random quotes in your header, this needs to be uncached, or you will just see the first random result every time. In all other cases, use caching.
Also remember that every time you save a change in the manager, the cache will be wiped. That means that if you for example display the latest news-articles on your frontpage, this can still be cached because it will not display different content until you add/edit a resource, and then the cache will be cleared.
To sum it all up. Caching is GREAT and you should use it as much as possible. I usually make all my snippets/chunks cached, and if I crash into problems, that is the first thing I check.
Using caching makes your webserver respond quicker (good for the user) and produces fewer queries to the database (good for you). All in all. Caching is a gift. Use it.