I ran across an interesting bit of XML in Magento 2 when I was learning about their XML & cacheing structure.

<referenceContainer name="page.top">
    <block class="Magento\Theme\Block\Html\Topmenu" name="catalog.topnav" template="html/topmenu.phtml" ttl="3600"/>
    <container name="top.container" as="topContainer" label="After Page Header Top" htmlTag="div" htmlClass="top-container"/>
    <block class="Magento\Theme\Block\Html\Breadcrumbs" name="breadcrumbs" as="breadcrumbs"/>

Specifically, I was curious what “ttl” on a block level meant in M2.

<block ... name="catalog.topnav" ... ttl="3600"/>

TTL is obviously time-to-live, and is the amount of time before a cached asset becomes invalidated and needs to be reloaded.

But why is it a property on the block level in Magento 2?

Turns out, when a page request is made for a Magento 2 site, only 95% of a page’s content is loaded from the server in the initial page request.

The other 5% is loaded by an AJAX request through knockout.js. (lots more posts on knockout in M2 coming soon)

Well, good luck finding more information on how that works, because Magento’s developer docs don’t cover it.

The 95% that is loaded by the server consists of lots & lots of individual blocks that combine to create the page’s HTML, and those blocks can be cached.

In Magento 2, elements can be cached on a block level.

My research led me to Alan Kent’s kickass blog post about M2 cacheing.

Individual blocks in M2’s XML structure can be given individual expiration dates, by setting different TTL values on the block declarations.

Declaring a block like so:

<block ... name="catalog.topnav" ... ttl="3600"/>

Will create the block and give it a lifetime of 60 hours (3600 seconds / 60 seconds) on the server (note, this is completely separate from client side cacheing).

After that expiration period, the next request for that block will invalidate that cached block and generate a new one.

For more information on cacheing in Magento 2, check out Alan Kent’s previously mentioned awesome blog post.