Caching

Caching in TYPO3

TYPO3 uses multiple caching strategies to ensure fast content delivery. Depending on the content a page contains, TYPO3 chooses the best caching strategy for that use case.

For example, you might have a fully-cacheable page, a page that is at least partially cacheable or a page that is completely dynamic. Dynamic elements in TYPO3 are also known as USER_INT or COA_INT objects - as these are the matching Typoscript objects used to render non-cacheable content.

When visiting a TYPO3 web site, TYPO3 knows the following states:

• first time hit, page has never been rendered ("cache miss")
• consecutive hit, page has been rendered before ("cache hit")

In the first case, TYPO3 renders the complete page and writes cache entries as configured. In the second case, TYPO3 fetches those entries from the cache and delivers them to the user without re-triggering the rendering.

In that second case, either the page is fully cached and directly delivered from the cache, or the page has non-cacheable elements on it. If a page has non-cacheable elements, TYPO3 first fetches the cached part of the page and then renders all dynamic parts.

Caching variants - or: What is a "cache hash"?

TYPO3 ideally delivers fully cached pages for maximum performance. However, in scenarios where the same page will deliver different content depending on URL parameters, TYPO3 needs a possibility to identify these "variants" and cache each of them differently. For example, if you have a news plugin and a detail page, the detail page is different for every news entry.

To identify the variant, TYPO3 combines a set of parameters and generates a hash value as identifier. These parameters include by default:

• id: The current page ID
• type: The current page type (typeNum)
• groupIds: The user groups of the logged-in user (if no user is logged in: 0, -1 as default values)
• MP: The mount point identifier
• site: The current site and base URL
• staticRouteArguments: Any route argument configured in the routing configuration and resolved in the current request
• dynamicArguments: Any "GET" parameters influencing the rendered page

Imagine the following URL https://example.org/news/?tx_example_news[id]=123 displaying the news with ID 123. If TYPO3 would cache that page with that parameter without any security mechanisms, it would open a potential denial of service attack as an unlimited amount of cache entries could be generated by adding arbitrary parameters. To avoid that, TYPO3 generates a so-called "cHash" parameter, which is a hash that basically signs the valid parameters for that request. So any parameter that validly influences the rendered page needs to be part of that cHash.

With routing you can configure TYPO3 not to display the cHash in your URLs in most cases. Routing adds an explicit mapping of incoming readable URL slugs to internal parameter values. This both adds an additional layer for validating slugs as well as reduces the parameters to a limited (and predictable) set of values.

Various configuration options exist to configure the cHash behavior via $GLOBALS['TYPO3_CONF_VARS']['FE']['cacheHash'] in the file config/system/settings.php or config/system/additional.php:

All properties can be configured with an array of values. Besides exact matches (equals) it is possible to apply partial matches at the beginning of a parameter (startsWith) or inline occurrences (contains).

URL parameter names are prefixed with the following indicators:

• = (equals): exact match, default behavior if not given
• ^ (startsWith): matching the beginning of a parameter name
• ~ (contains): matching any inline occurrence in a parameter name

These indicators can be used for all previously existing sub-properties cachedParametersWhiteList, excludedParameters, excludedParametersIfEmpty and requireCacheHashPresenceParameters.

Example (excerpt of config/system/additional.php)

$GLOBALS['TYPO3_CONF_VARS']['FE']['cacheHash'] = [
    'excludedParameters' => [
        'utm_source',
        'utm_medium',
    ],
    'excludedParametersIfEmpty' => [
        '^tx_my_plugin[aspects]',
        'tx_my_plugin[filter]',
    ],
];

For instance instead of having exclude items like

'excludedParameters' => [
    'tx_my_plugin[data][uid]',
    'tx_my_plugin[data][category]',
    'tx_my_plugin[data][order]',
    'tx_my_plugin[data][origin]',
    // ...
],

partial matches allow to simplify the configuration and consider all items having tx_my[data] (or tx_my[data][ to be more specific) as prefix like

'excludedParameters' => [
    '^tx_my_plugin[data][',
    // ...
],

Clearing/flushing and warming up caches

TYPO3 provides different possibilities to clear all or specific caches. Depending on the context, you might want to

• clear the cache for a single page (for example, to make changes visible)
• clear the frontend cache (for example, after templating changes)
• clear all caches (for example, during development, when making TypoScript changes)
• clear all caches incl. dependency injection (mainly useful during development)

Clearing the cache for a single page is done by using the "clear cache button" on that page in the backend (usually visualized with a "bolt" icon). Depending on user rights this option is available for editors.

Clearing the frontend caches and all caches can be done via the system toolbar in the TYPO3 backend. This option should only be available to administrators. Clearing all caches can have a significant impact on the performance of the web site and should be used sparingly on production systems.

The "fullest" option to clear all caches can be reached via the System Tools > Maintenance section. In the development context when new classes have been added to the system or in case of problems with the system using this cache clearing option will clear all caches including compiled code like the dependency injection container.

vendor/bin/typo3 cache:flush

typo3/sysext/core/bin/typo3 cache:flush

cache:flush [--group <all|system|di|pages|...>]

vendor/bin/typo3 cache:warmup

typo3/sysext/core/bin/typo3 cache:warmup

cache:warmup [--group <all|system|di|pages|...>]

Caching framework

TYPO3 contains a data caching framework which supports a wide variety of storage solutions and options for different caching needs. Each cache can be configured individually and can implement its own specific storage strategy.

The caching framework exists to help speeding up TYPO3 sites, especially heavily loaded ones. It is possible to move all caches to a dedicated cache server with specialized cache systems like the Redis key-value store (a so called NoSQL database).

Major parts of the original caching framework were originally backported from TYPO3 Flow.