If you are planning an upgrade from Drupal 8 to Drupal 9, I strongly recommend that you uninstall the contrib module multiversion before you update the core to the latest 9.x version.
1. Install the Multiversion Remover.
The module Multiversion Remover plays an important role on this process, so we need to install it:
composer require 'drupal/multiversion_remover:1.0.x-dev@dev'
drush en multiversion_remover -y
2. Delete replication, replication_log and workspace entities.
Go to the following URLs and delete all the entities:
3.-Implement a hook update.
Copy the code from this repo and paste it in a hook update in one of your custom modules.
Clear caches from the backend
https://YOUR-SITE-URL/admin/config/development/performance or using the terminal
4.- Run the Drupal updates
We need to execute the hook update that we implemented in the previous step, so we have to run the drupal updates from the browser https://YOUR-SITE-URL/update.php or using the terminal
drush updb -y
Important: While the updates are running, we need to check if the entities that we deleted in a previous step are not recreated, otherwise, we will have to re-delete them.
Remember, it has to be done before the updates process ends.
URLs to check if the entities were not re-created while running the updates:
Most likely, you will get an error, that is ok.
5.- Execute multiversion remover functions.
You need to execute the following commands, to complete the removal process:
drush php-eval "multiversion_remover_uninstall_multiversion_suite()"
drush php-eval "_multiversion_remover_purge_multiversion_kvp()"
6.- Uninstall the Multiversion Remover module.
At this point, the Multiversion Remover module did its job and we can remove it from the project.
drush pmu multiversion_remover -y
composer remove drupal/multiversion_remover