How to clean up nextcloud-data/appdata_* and /updater-*

[gas85]

As I linked above you can adjust config, my current config is:

@gas85

  'enable_previews' => true,
    'enabledPreviewProviders' => 
    array (
      0 => 'OC\\Preview\\PNG',
      1 => 'OC\\Preview\\JPEG',
      2 => 'OC\\Preview\\GIF',
      3 => 'OC\\Preview\\BMP',
      4 => 'OC\\Preview\\XBitmap',
      5 => 'OC\\Preview\\Movie',
      6 => 'OC\\Preview\\PDF',
      7 => 'OC\\Preview\\MP3',
      8 => 'OC\\Preview\\TXT',
      9 => 'OC\\Preview\\MarkDown',
    ),
    'preview_max_x' => 1080,
    'preview_max_y' => 1920,
    'jpeg_quality' => 90,

Read more about:
https://ownyourbits.com/2019/06/29/understanding-and-improving-nextcloud-previews/

And than you need to regenerate previews again:

@gas85

P.S. It turns that changing of config.php will not automatically recreate smaller/bigger previews. This is how to do it https://github.com/rullzer/previewgenerator/issues/94#issuecomment-355745556 run pregenerate command afterwards.

Short summery from the Github:

To “reset” the preview cache

1. Stop Webserver (apache / nginx)
2. Moved the appdata_instaceName/preview folder outside the appdata folder. You can just remove it if you are confident.
3. Run sudo -u www-data /usr/bin/php /var/www/nextcloud/occ files:scan-app-data to fix database
4. Start Webserver and Test everything works
5. Finish up (delete moved folder, etc).
6. Run pregenerate command afterwards.