I sent an ALTER statement that took a long time and I killed some minutes after and then I noticed that CPU usage is almost 100% (98%, 99%, etc).

The process is still being listed with "Killed" status. Reading some answers here, I understand that a killed process can take a long time because it needs to do some rollbacks.

But I didn't get why the database is still running and responding to the application with almost 100% of CPU usage. There are some kind of prioritization on the database tasks?


  • Do you only have one CPU core on your server? If it weren't a killed process but instead another process running a query simultaneously (or another application connection), would you still be surprised that those connections didn't block each other?
    – mustaccio
    Aug 15, 2022 at 18:50
  • Thanks for your answer, I have 2 cores, you meant that the 100% CPU usage info on AWS refers to a single CPU? Tks! Aug 15, 2022 at 19:02
  • When you have 2 cpu's in linux, they believe you have 200% available. And you do since 1 cpu can be busy 100% and the other cpu can be busy 100%. Aug 15, 2022 at 21:34
  • When you have the opportunity to use an 8 cpu in linux you could find 800% busy reported. Aug 15, 2022 at 21:35
  • What was the ALTER statement? Which version of MySQL? Both can make a big difference in how to answer your question.
    – Rick James
    Aug 15, 2022 at 23:10

1 Answer 1


You can set below parameter value if you have 2 core cpu :

innodb_thread_concurrency = CPU * 2

Default value is 0, A value of 0 (the default) is interpreted as infinite concurrency (no limit). This variable is intended for performance tuning on high concurrency systems

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