Removing phantom plugin from database

On several sites I've worked on, for whatever reason before I put my hands on it, the database seems to register a plugin that is no longer in config or code.

This usually goes as follows:

[error] Drupal\Component\Plugin\Exception\PluginNotFoundException: The "name-of-plugin" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager->getDefinition()

In D7, it was relatively straightforward to delete offending module entries from the database. What tables store plugin data so I can tell Drupal to stop looking for them and whitescreening when they can't be found?

Export the entire config, either in UI or via drush cex. Then make a full-text search for the plugin name. Remove the configuration causing the error and import the config again drush cim.

BTW if you turn on full error messages at admin/config/development/logging you see more info on which code is trying to load the plugin. This can point to a code line using a config object or a hard-coded plugin name.

If you can't access the admin UI because of the error add this option to settings.php:

/**
 * Show all error messages, with backtrace information.
 *
 * In case the error level could not be fetched from the database, as for
 * example the database connection failed, we rely only on this value.
 */
$config['system.logging']['error_level'] = 'verbose';

Or activate web/sites/example.settings.local.php from where this is copied.