Slow extendedconfirmeds on enwiki

SQL

SELECT user_name, user_registration, log_timestamp, log_timestamp - user_registration AS time_between
FROM logging
	INNER JOIN user ON user_name = REPLACE(log_title, "_", " ")
WHERE log_type = "rights"
	AND REGEXP_SUBSTR(LOG_PARAMS, 'oldgroups";a:\\d+:\\K.*?\\}') NOT LIKE "%extendedconfirmed%"
	AND REGEXP_SUBSTR(LOG_PARAMS, 'newgroups";a:\\d+:\\K.*?\\}') LIKE "%extendedconfirmed%"
    AND EXISTS ( -- Anyone who's since lost it will be a weird fluke of some sort
      SELECT 1
      FROM user_groups
      WHERE ug_user = user_id
      	AND ug_group = "extendedconfirmed"
    )
    AND NOT EXISTS ( -- Delayed grant due to adminship at time of EC implementation.
      SELECT 1
      FROM user_former_groups
      WHERE ufg_user = user_id
      	AND ufg_group = "sysop"
    )
ORDER BY 4 DESC
SQL

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