"Refill event streams" stops after a few seconds with "undefined"

Question

When I click "Refill event streams" on Admin > Stats, it works for a few questions then just says "undefined". I turned on error logging and didn't see anything when I run it.

I checked the AJAX requests in Chrome. Here are the last two responses, the first one working fine and the second one causing the error.

QA_AJAX_RESPONSE
1
dorefillevents_refill,15499,213,45
Refilled for 45 of 15,499 questions...

QA_AJAX_RESPONSE
0
A database error occurred.

Also just to add, after this happened I tried again with maintenance mode running, just in case it was due to a user adding a post. Still had the problem.

Comments

There should be a corresponding error in your server's error_log file?

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OK I assumed it would be the PHP error log, but there is this in the Apache error log:

PHP Question2Answer MySQL query error 1452: Cannot add or update a child row: a foreign key constraint fails (`pokemondb`.`qa_userevents`, CONSTRAINT `qa_userevents_ibfk_1` FOREIGN KEY (`userid`) REFERENCES `qa_users` (`userid`) ON DELETE CASCADE) - Query: INSERT INTO qa_userevents (userid, entitytype, entityid, questionid, lastpostid, updatetype, lastuserid, updated) VALUES ('87', '-', 0, 249, 2960, NULL, '229', FROM_UNIXTIME(1278214178)), referer: mysite/pokebase/admin/stats

BTW I ran the script on my "meta" site with no problems. Is this another "legacy" problem, from the Q2A database structure changing over the versions?

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From the error you posted, it seems like this is happening because an event is being created for a user (userid 87) based on some prior activity of that user referenced in the database, but the user has been deleted. Can you please check if there is a row in qa_posts with userid set to 87 and confirm that there is no row in qa_users with that userid? Perhaps you deleted the user manually some time ago, before Q2A offered a user delete facility? If so the solution is to set the userid or lastuserid of any row in qa_posts to NULL, if it contains 87.

Answer 1

Followed gidgreen's advice in the comment. I don't remember manually deleting any users but user #87 was missing and had a userid in the qa_posts table. Setting that to NULL allowed the event streams to continue OK.

I double checked all the other deleted users as well.