I have a high concurrency mysql 8.0 server.
Thousands of tasks happen per second (up to a million rows per second read in average)
In some of the tasks that can be very performance intense I have an emergency switch to prevent the database queue from overflowing.
I read the number of processes (sometimes specific ones) from information_schema.processlist and if they exceed a certain value the task is skipped until the database is back in time.
So much so good, that worked perfectly fine in mysql 5.7 and before, but in mysql 8.0 they removed the query cache which might be the reason why it can not deliver such performance anymore.
In my case the server quickly is overflown with these SELECTS.
So I decided to run a background task that refreshes a table every second with a dump of the processlist.
I am using Innodb as MEMORY has more blocking issues.
This is the syntax I run every second: processlist is "LIKE information_schema.processlist but I've changed the Info blob to a varchar"
BEGIN; truncate table processlist; replace into processlist SELECT ID,USER,HOST,DB,COMMAND,TIME,STATE,LEFT(INFO,1024) AS INFO FROM information_schema.processlist WHERE Command != 'Sleep'; COMMIT;
I am using a transaction to prevent race conditions and just truncate + replace into.
However I am not sure if this is the best solution to populate a "mirror" table.
So my question is: is this a good approach (especially not sure what truncate might mean on performance) ? Any ideas how to do this better ?