This adds an option to the prune_objects mix task.
The original way deleted all non-local public posts older than a certain time frame.
Here we add a different query which you can call using the option --keep-threads.
We query from the activities table all context id's where
1. the newest activity with this context is still old
2. none of the activities with this context is is local
3. none of the activities with this context is bookmarked
and delete all objects with these contexts.
The idea is that posts with local activities (posts, replies, likes, repeats...) may be intersesting to keep.
Besides that, a post lives in a certain context (the thread), so we keep the whole thread as well.
Caveats:
* Quotes have a different context. Therefore, when someone quotes a post, it's possible the quoted post will still be deleted.
* Although undocumented (in docs/docs/administration/CLI_tasks/database.md/#prune-old-remote-posts-from-the-database), the 'normal' delete action still keeps old remote non-public posts. With this option we don't care about scope.
* I ran this on my instance, but directly on the DB. I still need to test to be sure that we don't get a time-out error or something.
Some statistics from explain analyse:
(cost=1402845.92..1933782.00 rows=3810907 width=62) (actual time=2562455.486..2562455.495 rows=0 loops=1)
Planning Time: 505.327 ms
Trigger for constraint chat_message_references_object_id_fkey: time=651939.797 calls=921740
Trigger for constraint deliveries_object_id_fkey: time=52036.009 calls=921740
Trigger for constraint hashtags_objects_object_id_fkey: time=20665.778 calls=921740
Execution Time: 3287933.902 ms
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