===== Fehlender Index in Datenbank =====
  Fehlender Index "fs_storage_path_prefix" in der Tabelle "oc_filecache".
  Fehlender Index "fs_id_storage_size" in der Tabelle "oc_filecache".
  Fehlender Index "properties_pathonly_index" in der Tabelle "oc_properties".
  Fehlender Index "job_lastcheck_reserved" in der Tabelle "oc_jobs".

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===== Memcache \OC\Memcache\APCu not available for local cache =====
  * ERROR:<code>OC\HintException: [0]: Memcache \OC\Memcache\APCu not available for local cache (Is the matching PHP module installed and enabled?)</code>
  * FIX:<code bash>nano /etc/php/x.x/cli/php.ini -> append "apc.enable_cli = 1"
cd /var/www/html/nextcloud</code><code>sudo -u www-data php occ db:add-missing-indices</code>

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===== Prepare Update =====
  * comment out createBackup in updater.php<code php>
case 3:
  //$updater->createBackup();
  break;
</code>

===== Remove e2e folder =====
  * Disable e2e plugin
  * delete all encrypted folders (via ssh)
  * remove ''appdata_[your installation id]/end_to_end_encryption/*''
  * ''mysql> oc_e2e_encryption_lock;''
  * ''DELETE FROM oc_filecache WHERE path LIKE "%[your old e2e folders]%";''