Performing some computations in Zope can take a long time or use a lot of resources. One way to deal with expensive tasks is to cache them. The first time the computation is requested, the results are stored in a table or cache. Subsequent requests get the results from the cache. This can result in a dramatic speed increase.
There are so many possible strategies for caching that no one could possibly come up with them all. Caches can be stored in memory, on disk, on other computers, or by other means. Caches can be limited in size or unconstrained. They can be made to work with only specific types of objects. They can be tuned in different ways.
So instead of trying to provide for every possible caching strategy, Zope defines an API called cache management that lets developers write their own caching strategies, or cache managers, and lets site administrators easily connect cacheable objects to those cache managers.
You can use caching to speed up access to often-requested pages, reduce disk access and network traffic, and deal with heavy loads. All these benefits come with risks of excessive caching, however, so it's important to fine-tune the cache settings. More on this later.
The first thing you need to do is create a cache manager instance.
In the Zope management interface, go to a folder containing objects
that would benefit from caching. From the add list, select a
cache manager type such as
RAM Cache Manager. Use an ID that
describes the purpose of the cache manager.
Next, visit one of the objects that you want to cache. A new tab
Cache should be visible. Select it. From the drop-down
box, select the cache manager you just created and press the
The object is now ready to be cached. Visit the
View tab. If
the object is a script that takes a long time to render, the first
view will still take just as long as before. But if you're using
a RAM cache manager or similar, the second view should be much faster.
Press the reload button in your browser to try it out.
You can associate many objects to a cache manager at once using the
Associate tab of all cache managers. Visit the cache manager
object you created and select the
Associate tab. Press the
Locate button. Zope will locate all cacheable objects in the
folder. Select the checkboxes next to the objects you want to
cache and press the
Save changes button.
Cache managers generally don't know the nature of what is being cached, so here are some issues that can surface:
Because of these risks, you should be careful when setting up caching. You'll need to fine-tune the cache settings. Sometimes you'll find that you can't cache one of your major pages, but that you can cache pieces of it.
Also remember that caching can actually slow down Zope if it is applied unscrupulously. You should perform speed tests to verify that caching really does speed up your site.