The Flex cache is used to improve performance of your website. In OpenCms pages are typically built on-the-fly when requested. This involves many costly steps, e.g., database queries. To obtain a performant web site, caching is essential.
Not every resource's output HTML should be cached the same way. E.g., navigation content's HTML output used on many pages should be rendered and cached for each page separately, a function that outputs date and time should be rendered on every request, a completely static content item should be rendered only once, equally at which page it is used, etc. The Flex cache is the tool to configure caching in a resource specific way.
The Flex cache is enabled or disabled in the configuration file /WEB-INF/config/opencms-system.xml of your OpenCms web application. There are two options to set the FlexCache:
Here's the default configuration in /WEB-INF/config/opencms-system.xml:
<flexcache>
<cache-enabled>true</cache-enabled>
<cache-offline>false</cache-offline>
<maxcachebytes>8000000</maxcachebytes>
<avgcachebytes>6000000</avgcachebytes>
<maxentrybytes>400000</maxentrybytes>
<maxkeys>2000</maxkeys>
</flexcache>Enables or disables the Flex cache. If you disable the Flex cache, you do not need to bother about the settings of the other Flex cache values.
The following values are possible:true (default): The Flex cache is enabled.false: The Flex cache is disabled.
In a development environment, we recommend to set the value of the cache-offline node to true so that you can test out the caching behaviour of the application without publishing. In a production environment you should set cache-offline node to false. The following values are supported:true: The Flex cache for offline projects is enabled.false (default): The Flex cache for offline projects is disabled.
The default settings of the Flex cache parameters after installing OpenCms are:
The following table lists all possible FlexCache directives. These directives must be attached to a specific page using the cache property. In case you want to set more than one directive, use a semicolon ";" to separate them.
This resource is not cachable. Nothing will be cached under any circumstance. This overrides all other directives that might also be given.
This resource is cachable and there will always be the same result generated for all requests, i.e., only one variation entry for the page will be saved in the cache. This overrides all other directives (other than never and no-params) that might also be given.
One variation entry of this resource is generated for every different user. Please keep in mind that this might lead to a great number of entries in the cache in case you have a website with many different users. You should know that any client not authorized is treated in OpenCms as user "Guest", so all requests always belong to a specific user.
One variation entry of this resource is generated for every "top level" URI that is requested. This is useful for navigation elements that are included as a sub-element on a page, where usually the URI of the requested page decides which entries have to be displayed in the navigation.
This directive sets a timeout at which a cached resource will be invalidated. The given integer represents a minute - interval which starts at 0.00h of the day the cache key gets calculated. A value of 60 would indicate that this entry will reach its timeout at the beginning of every full hour. A timeout of 20 indicates that the entry is invalidated at x.00, x.20 and x.40 of every hour etc. A "timed out" resource will stay in the cache but will be re-calculated the next time it gets requested.
If you use attrs=(attr1, attr2,...) there will be one variation entry generated for every value of all listed request attributes (or combination thereof). If you use attrs there will be one variation entry of this resource generated for every different attribute value of every different attribute.
This directive prevents the caching of a resource. If you use no-attrs the occurrence of any attribute in the request will prevent caching of the resource. If you use no-attrs=(no-attr1, no-attr2,...), the occurrence of any of the listed parameters will prevent caching of the resource. Note that these "blocking" directives always overrule all other directives.
If you use params=(param1, param2,...) there will be one variation entry generated for every value of all listed parameters (or combination thereof). If you use params there will be one variation entry of this resource generated for every different parameter value of every different parameter. This directive is useful if you have something like a "show article" page that gets dynamically calculated from a database with something like an "id" parameter that selects the article to be displayed. So if you have a page showarticle.jsp that gets usually called like showarticle.jsp?article_id=123, you could just set the caching properties of this page to params=(article_id) and thus cache every single article page.
This directive prevents the caching of a resource. If you use no-params the occurrence of any parameter in the request will prevent caching of the resource. If you use no-params=(no-param1, no-param2,...), the occurrence of any of the listed parameters will prevent caching of the resource. This directive is useful on simple forms. Usually (esp. using JSPs) you will have only one URI for all requests to the form, i.e., the form is posted to its own URL and the JSP behind it handles the form validation. With the no-params directive you can cache the "first", empty view of the form, while any requests with data in the form will cause the page to be generated dynamically. Note that these "blocking" directives always overrule all other directives.
This cache directives creates one variation of a page for every element. This important directive is required if multiple xmlpage elements are included from the same URI. It ensures that changes in the listed sub-elements will result in an update of the including page.
This directive creates one variation entry of the resource for every locale value. This cache directive is nescessary, if locale-based localization is used for elements that are used in different language variations.
One variation entry of the resource is created for every encoding value. If a sub-element is used with different encodings in different parts of a site, the caching must be encoding dependent.
This directive causes a variation to be generated for every (or every listed) request scheme. The most often used request schemes are currently "http" or "https".
This directive causes a variation to be generated for every listed server TCP port of the request. This might come handy in complex OpenCms setup scenarios where a server is addressed by multiple ports.
If you use session=(attribute1, attribute2,...) there will be one variation entry generated for every value of all listed session attributes (or combination thereof). You must at least use one attribute value.
If you use site there will be one variation entry generated for every OpenCms site. This can be used to cache site-specific elements, e.g., template heads with logos, etc.
This directive causes a variation to be generated for every client ip addresses of the request. This enables a caching based on different client locations.
To be used together with formatter JSPs. Use this directive to ensure that an element is rendered correctly inside a container, if it occurs several times on a single page inside different containers.
To be used when JSPs render device specifically, either by evaluating the template context via the provider or the <cms:device> tag. The directive causes the flex cache to cache different versions of HTML output for different contexts.
Flex cache buckets were introduced in OpenCms 11 to improve the performance of the Flex cache. The motivation is as follows: In the default scenario without buckets, the flex cache is completely flushed on each publish event. It does not matter if the published resources will change the cached JSP output or not. To reduce the need of rendering all JSPs again after a publish event, it would be great to selectively flush only parts of the Flex cache, depending on the resources that are published.
Unfortunately, it is not possible to calculate which change at which resource influences the output of which JSP in general. But, to some extend we can assume what changes cannot influence the output of what JSPs. In the bucket scenario, we explore the caching directives set at the JSPs for the assumptions.
Buckets, introduced in OpenCms 11, are configured by placing the file flexconfig.properties under /system/config/. The file holds the bucket configuration as key-value pairs. Typically, you configure one bucket per site, e.g.:
bucket.baz=/sites/baz/,/shared/
bucket.bar=/sites/bar/,/shared/
bucket.foo=/sites/foo/,/shared/In the example, we make up three buckets and assign a list of VFS root paths to each of them. Here, the path to a site ("bar", "baz" and "foo") and the path to the shared folder is added to each of them. Implicitly, the configuration holds as well:
OTHER that is configured for all VFS root paths not in any other bucket, i.e., not a (sub-)path of the paths configured for any other bucketclearAll=/system/modules entry - which can be overwritten by an explicit configuration.When a publish event occurs, the Flex cache entries are flushed depending on the buckets they belong to. In particular, an entry is deleted if:
clearAll is published.In our example configuration this means in particular, that publishing changes in site "baz" will not flush the buckets for sites "bar" and "foo".
Which flex cache entry goes to which bucket(s) is determined by the cache directives set at the JSP whose output is cached. In particular, path information contained in the flex directive is explored. The scenario is as follows:
Path information is contained in multiple flex cache directives, e.g., uri or container-element. But there are also directives that contain no path information, e.g. always. For such, the Flex cache entries are added to no bucket at all and thus they are removed from the cache on each publish event.