silverstripe-framework/docs/en/02_Developer_Guides/01_Templates/07_Caching.md

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title: Caching summary: Reduce rendering time with cached templates and understand the limitations of the ViewableData object caching.

Caching

Object caching

All functions that provide data to templates must have no side effects, as the value is cached after first access. For example, this controller method will not behave as you might imagine.

:::php
private $counter = 0;

public function Counter() {
    $this->counter += 1;

    return $this->counter;
}


:::ss
$Counter, $Counter, $Counter

// returns 1, 1, 1

When we render $Counter to the template we would expect the value to increase and output 1, 2, 3. However, as $Counter is cached at the first access, the value of 1 is saved.

Partial caching

Partial caching is a feature that allows the caching of just a portion of a page. Instead of fetching the required data from the database to display, the contents of the area are fetched from a cache backend.

:::ss
<% cached 'MyCachedContent', LastEdited %>
	$Title
<% end_cached %>