All persistent configuration for the caching machinery is stored in the
configuration registry, as managed by
plone.app.registry. This can be
modified using the
registry.xml GenericSetup import step. The Import
settings tab of the control panel allows you to import these caching
Default caching profiles¶
plone.app.caching includes three default caching profiles. Two of these
profiles encapsulate the cache settings that are known to work well with a
typical default Plone installation. The third is an example profile for a
“split-view” caching setup (see the split-view discussion later in this
The three default caching profiles:
- Without caching proxy
Settings useful for setups without a caching proxy.
- With caching proxy
Settings useful for setups with a caching proxy such as Squid or Varnish. The only difference from the “without caching proxy” profile are some settings to enable proxy caching of files/images in content space and content feeds.
- With caching proxy (and split-view caching)
An example profile for a caching proxy setup with split-view caching enabled. This example requires a special proxy setup.
Custom caching profiles¶
Caching policies are often a compromise between speed and freshness. More aggressive caching often comes at the cost of increased risk of stale responses. The default profiles provided tend to err on the side of freshness over speed so there is some room for tweaking if greater speed is desired.
Customization may also be needed if third-party products are installed which require special treatment. Examine the HTTP response headers to determine whether the third-party product requires special treatment. Most simple cases probably can be solved by adding the content type or template to the appropriate mapping. More complicated cases, may require custom caching operations.
A GenericSetup profile used for caching should be registered for the
ICacheProfiles marker interface to distinguish it from more general
profiles used to install a product. This also hides the profile from
Plone’s Add-ons control panel.
Here is an example from this package:
<genericsetup:registerProfile name="with-caching-proxy" title="With caching proxy" description="Settings useful for setups with a caching proxy such as Squid or Varnish" directory="profiles/with-caching-proxy" provides="Products.GenericSetup.interfaces.EXTENSION" for="plone.app.caching.interfaces.ICacheProfiles" />
profiles/with-caching-proxy contains a single import step,
registry.xml, containing settings to configure the ruleset to operation
mapping, and setting options for various operations. At the time of writing,
<record name="plone.caching.interfaces.ICacheSettings.operationMapping"> <value purge="False"> <element key="plone.resource">plone.app.caching.strongCaching</element> <element key="plone.stableResource">plone.app.caching.strongCaching</element> <element key="plone.content.itemView">plone.app.caching.weakCaching</element> <element key="plone.content.feed">plone.app.caching.moderateCaching</element> <element key="plone.content.folderView">plone.app.caching.weakCaching</element> <element key="plone.content.file">plone.app.caching.moderateCaching</element> </value> </record>
Default options for the various standard operations are found in the
registry.xml file that is part of the standard installation profile for
this product, in the directory
profiles/default. The custom profile
overrides a number of operation settings for specific rulesets (see below).
<record name="plone.app.caching.weakCaching.plone.content.itemView.ramCache"> <field ref="plone.app.caching.weakCaching.ramCache" /> <value>True</value> </record>
This enables RAM caching for the “weak caching” operation for resources using
plone.content.itemView. The default is defined in the main
<record name="plone.app.caching.weakCaching.ramCache"> <field type="plone.registry.field.Bool"> <title>RAM cache</title> <description>Turn on caching in Zope memory</description> <required>False</required> </field> <value>False</value> </record>
Notice how we use a field reference to avoid having to re-define the field.
It may be useful looking at these bundled
registry.xml for inspiration if
you are building your own caching profile. Alternatively, you can export the
registry from the
portal_setup tool and pull out the records under the
registry.xml is all that is required, but you are free to add
additional import steps if required. You can also add a
use the GenericSetup dependency mechanism to install other profiles on the