Auto deletion of tasks

text/0060-tasks-api.md

@@ -4,7 +4,7 @@
 
 ### I. Summary
 
-This specification describes the API endpoints for handling asynchronous tasks.
+This specification describes the behaviour of the task queue and the API endpoints for handling asynchronous operations.
 
 ### II. Motivation
 
@@ -1008,10 +1008,22 @@ The task types are listed in decreasing order of priority:
 4. `dumpCreation`
 5. All other task types with by their enqueued at order.
 
+### 2.2. Auto deletion of tasks
+
+Since Meilisearch can't store tasks forever, at some point, it needs to free up some space in its queue.
+The engine will try to delete the 100k last finished tasks upon reaching 1M total tasks stored.
+
+That means after a batch finishes processing and right before processing the following enqueued tasks,
+Meilisearch will check the number of tasks currently written in its queue.
+If this number is more than 1M, the engine will enqueue a new task that automatically deletes
+the last 100k **finished** tasks.
+That means if there are only 2k finished tasks, only these ones will be deleted.
+And if all the tasks in the queue are still enqueued, then nothing will be deleted, and the engine
+will continue to process the next enqueued tasks.
+
 ## 3. Future Possibilities
 
 - Use Hateoas capability to give direct access to a `task` resource.
 - Add dedicated task type names modifying a sub-setting. e.g. `SearchableAttributesUpdate`.
-- Add an archived state for old `tasks`.
 - Add the `API Key` identity that added a `task`.
 - Make dump import visible as a task.