A lot of very interesting things are happening to make Drupal's caching system a bit smarter. One of my favorite recent (albeit smaller) developments is a patch (http://drupal.org/node/1471200) for the Views module that allows for cached views to have no expiration date. This means that the view will remain in the cache until it is explicitly removed.

Before this patch landed, developers were forced to set an arbitrary time limit for how long Views would store the cached content. So even if your view's content only changed every six months, you had to choose a time limit from a list of those predefined by Views, the maximum of which was 6 days. Every six days, the view content would be flushed and regenerated, regardless of whether its contents had actually changed or not.

The functionality provided by this patch opens the door for some really powerful behavior. Say, for instance, that I have a fairly standard blog view. Since I publish blog posts somewhat infrequently, I would only like to clear this view's cache when a new blog post is created, updated, or deleted.

To set up the view to cache indefinitely, click on the "Caching" settings in your view and select "Time-based" from the pop-up.

Then, in the Caching settings form that follows, set the length of time to "Custom" and enter "0" in the "Seconds" field. You can do the same for the "Rendered output" settings if you'd like to also cache the rendered output of the view.

Once you save your view, you should be all set.

Next, we need to manually invalidate the cached view whenever its content changes. There are a couple different ways to do this depending on what sort of content is included in the view (including both of the modules linked to above). In this case, I'll keep it lightweight and act on hooks in a custom module:

/**<br> * Implements hook_node_insert().<br> */<br>function MY_MODULE_node_insert($node) {<br>&nbsp; if ($node-&gt;type == 'blog') {<br>&nbsp;&nbsp;&nbsp; cache_clear_all('blog:', 'cache_views', TRUE);&nbsp; <br>&nbsp; }<br>}<br><br>...Same for hook_node_update() and hook_node_delete()...

And just like that, my view is only regenerated when it needs to be, and should be blazing fast in between.

The patch was committed to the 7.x-3.x branch of Views on March 31, 2012, so for now you will have to manually apply the patch until it is released in the next point release.

Happy caching!