wp-mu or large site may have problem with database cache funtion

if your site have new user register every 1-3 minute and you have enabled database cache then check your wp_users table in database regularly because plugin run query when user register again and again (run from cache in your ram that store for 180 second) so you’ll have many duplicate user in database

tick ” Don’t cache queries for logged in users” doesn’t work because user not logged-in when they register

fixed: put “users” in “Ignored query stems:” so plugin wont cache query when visitor register

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if your site have many users, you can run this query to check duplicate user

SELECT user_login, user_email, count(*)
FROM wp_users
GROUP BY user_login, user_email
HAVING count(*) > 1

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sometime database cache have problem with wp_comments too but only happen with very large site that have many comments

all regular sites not affected