Killing a MySQL query during execution with PHP and AJAX

Question

I am creating a custom query builder, when user has created his query he can verify the query syntax by clicking a button. When the user click on the button to verify, An A

Answer 1

You would have to allow the application to kill database queries, and you need to implement a more complex interaction between Client and Server, which could lead to security holes if done wrong.

The Start-Request should contain a session and a page id (secure id, so not 3 and 4 and 5 but a non-guessable but unique hash of some kind). The backend then connects this id with the query. This could be done in some extra table of the database, or a redis-way if you have redis anyway, but also via comments in the SQL query, like "Session fid98a08u4j, Page 940jfmkvlz" => s:p:.

/* s:fid98a08u4jp:940jfmkvlz */ select * from ...

If the user presses "Cancel", you send a Cancel-request with session and page id to the server. The php-code then fetches the list of your running SQL Queries with show processlist and searches for session and page to extract the query id.

Then the php sends a

kill query 

to the MySQL-server.

This might lead to trouble when not using transactions, and this might damage replication. And even a kill query might take some time in the state 'killing'.

So this should be the last possible of several variants. But sometimes it has to be done, I even had once a program where you could list your own running queries to kill them, which was needed because of "quotas" (you could not run more than two or three reporting requests at the same time).