Purge Queues

This module provides extra Purge queue plugins.

Database plugins

Purge module allows enqueueing duplicate items.
There's an issue to address this at https://www.drupal.org/node/2851893

While a general solution that works for all Purge queue implementations
is hard to implement, a specific change to the database plugin in order
to reject duplicate items is feasible.

This module provides two database plugins, database_alt and database_unique.

database_alt is an extension of the database plugin provided by Purge
module that works the same and additionally provides an extended schema
to store the invalidation type and expression in database columns.
Queue item data is not altered at all.

database_unique is an extension of the database_alt plugin that rejects
creation of duplicate items.