Caching is a crucial aspect of website performance optimization. It helps reduce the load on servers by storing copies of frequently accessed resources and serving them from memory or disk instead of generating them dynamically. In the Plone content management system, caching is managed by the plone.caching package. This article provides a comprehensive guide to using and customizing caching in Plone.
Installation and Configuration
To use plone.caching, you need to install it into your Plone build and load its configuration. You can install plone.caching by including it in your package’s setup.py file:
install_requires = [
...
'plone.caching',
]Next, load the package’s configuration from your package’s configure.zcml file:
After installation, you need to ensure that the cache settings records are installed in the registry. This can be done by registering a utility providing plone.registry.interfaces.IRegistry. For example, in a test environment, you can do the following:
from zope.component import provideAdapter
from plone.registry.interfaces import IRegistry
from plone.registry import Registry
provideAdapter(Registry(), IRegistry)Finally, you must add the plone.caching settings to the registry and enable the caching engine:
from zope.component import getUtility
from plone.registry.interfaces import IRegistry
from plone.caching.interfaces import ICacheSettings
registry = getUtility(IRegistry)
registry.registerInterface(ICacheSettings)
registry['plone.caching.interfaces.ICacheSettings.enabled'] = TrueCache Rules and Operations
The main concept in plone.caching is the cache rule set. A cache rule set is a collection of publishable resources (e.g., views) defined for caching purposes. You can declare cache rule sets in ZCML using the “ directive. Each rule set should have a unique name, which should be a dotted name consisting of letters, digits, underscores, and periods.
Cache rule sets are associated with caching operations. A caching operation is a component that modifies responses for caching purposes. In plone.caching, caching operations are named multi-adapters on the published object and the request. You can declare caching operations in ZCML using the “ directive.
To map cache rule sets to caching operations, you need to configure the operationMapping in the registry. This mapping is stored as a dictionary of dotted name strings, where the keys are the names of the rule sets and the values are the names of the caching operations.
Writing Custom Caching Operations
plone.caching provides a framework for writing custom caching operations. A caching operation consists of two components: a named multi-adapter implementing the operation itself and a named utility providing metadata about the operation.
To implement a caching operation, you need to create a class that implements the plone.caching.interfaces.ICachingOperation interface and the plone.caching.interfaces.ICachingOperationType interface. The ICachingOperation interface defines two methods: interceptResponse() and modifyResponse(), which are called at different stages of the request lifecycle.
For example, let’s say you want to create a caching operation that sets a fixed max-age cache control header. You can create a class that looks like this:
from plone.caching.interfaces import ICachingOperation
from plone.caching.interfaces import ICachingOperationType
from zope.interface import implementer
from zope.interface import Interface
@implementer(ICachingOperation, ICachingOperationType)
class MaxAge(object):
title = "Max age"
description = "Sets a fixed max age value"
prefix = 'my.package.operation'
options = ('maxAge',)
def __init__(self, published, request):
self.published = published
self.request = request
def interceptResponse(self, rulename, response):
maxAge = self.lookupOption(rulename, 'maxAge') or 3600
response.setHeader('Cache-Control', f'max-age={maxAge}, must-revalidate')
def modifyResponse(self, rulename, response):
passOnce you have implemented the caching operation, you can register it in ZCML using the and directives.
Conclusion
Caching plays a vital role in optimizing website performance, and plone.caching provides a powerful framework for managing caching in the Plone content management system. This article has covered the installation and configuration of plone.caching, the definition and mapping of cache rule sets to caching operations, and the creation of custom caching operations. By leveraging the caching capabilities of plone.caching, you can significantly improve the performance of your Plone websites.
If you have any questions or need further guidance, feel free to ask!
References:
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