Support » Plugin: Media Deduper » Further details on how this thing works

  • Resolved bkjproductions


    I see some of how this thing works thanks to your helpful FAQ’s. Can you supply a little more information, such as:

    • Does this create a table when you install it, and does it remove it when you uninstall? If it is adding metadata to the wp_posts table for each media item, is there a way to remove that metadata?
    • Does it look for the intermediate size images that WordPress creates (the Thumbnail and Medium and Large sizes), and does it delete them when it deletes an image? (Is it simply using the built-in WP function wp_delete_attachment that removes all derivatives?)
    • It looks like when MdD finds mypicture.jpg and mypicture1.jpg and both are 32652bytes, then that is flagged as a duplicate. What if someotherpicture.jpg is also 32652bytes, would all three of these images be considered duplicates?
    • To clarify the FAQ point about it detecting things only manually uploaded via the admin dashboard, does this look for loose files that are just sitting around in the wp-content/uploads/ folder that are not “properly” uploaded into WordPress (i.e. maybe someone naively dragged a bunch of jpgs into your uploads folder via Dreamweaver thinking they would magically appear in WordPress)? I suspect not but want to make sure.
    • It seems like it is doing some ajax requests when it reindexes, so what is the sort of load on the server you can expect? (Some of my shared hosting environments don’t seem to like it when a lot of ajax requests are made.)\
    • Is there a way to trigger a new scan? (I deactivated and reactivated and it seems to have the same database of files it found last time.)

    It looks like it is adding metadata to the wp_posts table,
    mdd_hash and

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  • Plugin Author Ben Byrne


    Hi there!

    Thanks for some great questions, I’ll answer them the best I can.

    • It does not create a table — as you identified, what it does is add two meta fields to wp_posts, mdd_hash and mdd_size. If Media Deduper is uninstalled, it should delete all those meta values. If you’re familiar with SQL it’s also pretty straightforward to remove them yourself if you need to.
    • Yes, Deduper utilizes WordPress’s native wp_delete_attachment function to delete items, which should delete all sizes.
    • No, Deduper is not just using the filesize to determine if two files are identical. It’s actually using an md5 hash of the file data itself, to avoid false matches like you describe.
    • You’re correct that it won’t find those — it only looks at files that are linked to attachment posts in the database, so something uploaded via FTP but not in the Media Library would be ignored.
    • Yes, Deduper uses AJAX to manage the indexing, with one AJAX request sent per item in the Media Library. Each AJAX call triggers calculating the filesize and md5 hash of the file, so it’s a bit resource-intensive but not terrible. Haven’t had reports of problems yet. Obviously we want to build and offer a good product that works for everyone, but tracking down specific problems with specific discount shared hosts can be quite tricky.
    • It’s on our roadmap to add a button or other feature to trigger a new scan, but right now there’s no convenient way to do it from the admin. If you properly uninstall the plugin, that should wipe out the metadata, or again if you’re savvy with SQL you could run a query to do it without having to uninstall.

    Hope that helps! Thanks for trying out Media Deduper.

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