Is it worth using cache warm up?

16.07.2019 Angelika Siczek
yellow letters cache on the back background

What is the cache warming up? It’s a cache memory warming process that developers use to improve website performance.


Many websites rely heavily on cache. It is a system that stores parts of a web page in high-performance mass memory. It is done to avoid loading information from low-performance systems or from parts of systems with lower bandwidth.


Cache files are present in many places when configuring the page. They can be found in processors, embedded in the database, as well as in applications such as Redis or Memcached.


cache warming up


How do I warm up the Varnish Cache cache?

In order to store data in the Varnish Cache, it must establish a connection to the main server. Each time TTL (time-to-live – period of validity of the data packet) expires, Varnish will delete it. To retain the storage of a data packet in its memory, another response must be made to the primary server’s query to receive the data.


How does cache warming work in practice?

In practice, heating the cache means that from time to time your data packets will load less due to data overdue. You will be asked again to download them to the main server. However, this slow response applies only to the first user, the rest will receive a packet straight from Varnish.


Warming Varnish Cache is a technique that prevents such situations by initiating these connections manually. You make a series of queries to your server about data packets and take the first slow loading, which will speed up the users’ use of the site.


However, continuous manual warm-up of the cache is an uninteresting activity. You do not want to sit on your website and click on each subpage.


What tools to warm up the cache are available?

There are many tools available on the Internet to warm up the cache. WGET is excellent. It has a command of recursiveness, which means that you can indicate any place on your site and have it download content from it. Later, he will scan the HTML page for each hyperlink that remains and download it as well.


What are the advantages of warming up the cache?

You can prepare your website by warming the cache for the coming of visitors. In this way, users will use fast loading and will not block your main server. The UX indicator will increase and the backend infrastructure will be protected.


What are the disadvantages of warming up the cache?

In practice, the cache will never cover all of the network traffic to which you will be exposed. Users will mainly use the main page  more often than for example a subpage about privacy protection. You will not have enough cache to cover all of your site’s data.


If you use the cache warm-up program, it will start from your home page, and then through links in HTML it will go further, without much logical order. Considering the Varnish Cache memory limitations, this means it will run out of the replacement server’s richness before it scans the entire page. It will start to overwrite the less needed further subpages on the page cache files on which you want more – those scanned at the beginning. This slows down the page again.


Later, you need to think about distributing cache files. If you warm up files in the Content Delivery Network (CDN), which PoP (Point from Presence) will choose your warming script? If you start warming up the cache from the central location, you will connect to the geographically closest server that is optimal for you. Then you warm up data packets for only one location.


And finally you have to think about the configuration of cache files. How do you configure them for users from other countries or different types of browsers?


You must also consider your vcl_hash file. If you have different versions of the site for different mobile devices, you must configure the crawler to handle the cache for all types of devices equally or according to preferences. Similarly, one should consider different language versions.


Is warming up the cache profitable?


To answer this question, consider the following issues:

1.What are the most important data packages to have in the cache?

2.What size is the cache memory?

3.If the cache is distributed in the CDN, which is the most important?

4.Do I need to know the cache configuration options?


The quickest answer will be that it causes more trouble than benefits. Warming up the cache in the natural environment will slightly deteriorate the page performance during page refresh. However, this is the best way to warm up the cache, because you do not have to worry about granting them priority or their configuration. Cache will adjust to the network traffic occurring on your website naturally and will set the priorities. However, if it is a solution that you still want to decide on, it is best if you first get acquainted with technical guides created by professionals or expert communities. There are also forums that will certainly help you in this regard.

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