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Pruning - what is it and how is it used?

Description: This is a quick tutorial on how to utilise the phpBB prune function.

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What is pruning?
Pruning is a function that automatically deletes older topics and thus ensures that the board does not become too large. It deletes all topics whose last post was more than a set number of days ago. Complete topics are always deleted, and only if all posts in the topic have exceeded the specified minimum age. For example, if a topic was created 102 days ago and a reply was created one day later, the topic will be deleted today during pruning if 100 days was set as the limit. However, if a new post was created yesterday, the entire topic remains and will be deleted in 99 days at the earliest (if the setting remains unchanged).

phpBB has a function that regularly checks the forums and, if necessary, automatically deletes older topics according to the settings made. In order to activate this function, the option "Activate automatic deletion of inactive topics" must be activated in the administration area under Forums (see there) "Manage forums" for each forum under Edit (green cogwheel) as well as the other settings must be made. The number of days after which a topic is to be deleted is set under "Days elapsed since last post" (see above). Under Check interval for automatic deletion, you can set how often a check should be made (see below). When a visitor visits the board, phpBB checks all forums for which automatic deletion is enabled, i.e. how many days have passed since the last pruning. If more days have passed than specified in the forum settings, phpBB will check all topics of the corresponding forums and delete them if the criteria mentioned apply.

Optimising prune settings
Which posts are to be deleted can be set as desired. However, the checking interval should be chosen so that not too many posts are deleted at once. Therefore, especially in forums with many posts, a low interval (possibly daily) should be selected.

Manual pruning
A pruning process can also be initiated manually via the menu item Manage forums (see there) "Prune forums". This is also possible if pruning has otherwise been deactivated in the administration area.

Announcements, polls and important topics
Announcements and polls as well as important topics have an additional option and are only deleted if this has also been set.

Pruning users
If you’ve been attacked by spambots see the How to clean up a board hit by spam KB article for suggestions how to use prune to clean up a board.

Originally published by on 10th Jun, 2020.