Difference between Drupal 8 and Drupal 9

Drupal 8 was released on 19 November 2015 and Drupal 9 was released on 3 June 2020.  Drupal 9 was built on version 8, so the changelog is shorter and the update from version 8 to 9 is simpler. The most important differences are the removal of almost all deprecated functions. In version 9, they've been replaced by other ones, and those that remained will be removed in the next installment of Drupal. A list of deprecated functions is available at Drupal.org. Also new in version 9 is the next version of Symfony. Drupal 8 used version 3, but now it's version 4. Additionally, the Twig theme engine version has been updated – has been changed from version 1 to 2. Another difference between Drupal 8 vs 9 is the fact that most of the jQuery UI library dependencies have been removed. In the case of performing tests, in the new version, we rely on the PHPUnit solution (previously, the SimpleTest framework could be used).

The next thing that was almost completely removed in Drupal 9 is the Simple Annotation Parser from Doctrine. However, the required elements were incorporated into the Drupal 9 core. We also need to pay attention to the Apache version, because in the case of Drupal 8 version 2.x was enough, but currently, Drupal 9 requires a min. version of 2.4.7. The situation is similar with PHP – this time a min. version of 7.3 is required, but version 7.4 and 8.0 are also supported (applies to Drupal 9.1.0). In terms of the database and the use of MySQL/Percona, Drupal 9 requires a min. version of 5.7.8; Drupal 8 worked with version 5.5.3. The same goes for using MariaDB and SQLite. These need to be min. versions of 10.3.7 and 3.26 respectively. The previous version of Drupal used version 5.5.20 for MariaDB and 3.6.8+ for SQLite.

Use Of Latest Versions Of Symphony Αnd Twig

Unlike Drupal 8 where Symphony 3 was used, Drupal 9 uses Symphony 4/5 for improving the website performance, scalability, quality, etc. Along with that, the new version uses Twig 2.0 as the templating engine.

Drupal 9 Is Backward Compatible

One of the major differences between the Drupal 9 upgrade from its predecessor upgrade is that it is backward compatible. If you have a fully updated Drupal 8 website, then it’s already compatible with the new version and can be easily upgraded. However, Drupal 8 wasn’t at all compatible with Drupal 7 and developers had a difficult time upgrading it to Drupal 8.

Upgraded Third-party Dependencies

Drupal 9 has also upgraded its third-party dependencies as it provides support for trusted third-party applications.

Performance

According to the above description of the differences between Drupal 8 vs 9, we can certainly say that the newer CMS release is much better in terms of speed. Using a min. PHP version of 7.3 improved the page loading speed. We can see an example on the PHP Benchmarks page, where all PHP versions are listed – from 5.6 to 8.0. At the very first glance, we can already see that between Drupal 8 and 9 there was an increase in performance of over 10%. This is the perfect reason to consider an upgrade, as each new version of PHP causes an even bigger leap in performance.

The situation is similar with Symfony. Version 3 has been used so far, but Drupal 9 needs the newer, fourth version of the framework. Thanks to it, we can significantly reduce the working time the developers need to create a new module or improve an existing one. The results of comparing Symfony versions from 2 to 5 can be checked on the already mentioned PHP Benchmarks page.