How to optimize COUNT(*) performance on InnoDB by using index

Question

I have a largish but narrow InnoDB table with ~9m records. Doing count(*) or count(id) on the table is extremely slow (6+ seconds):

Answer 1

Based on @Che code, you can also use triggers on INSERT and on UPDATE to perf2 in order to keep the value in stats table up to date.

CREATE TRIGGER `count_up` AFTER INSERT ON `perf2` FOR EACH ROW UPDATE `stats`
SET 
  `stats`.`value` = `stats`.`value` + 1 
WHERE
  `stats`.`key` = "perf2_count";

CREATE TRIGGER `count_down` AFTER DELETE ON `perf2` FOR EACH ROW UPDATE `stats`
SET 
  `stats`.`value` = `stats`.`value` - 1 
WHERE
  `stats`.`key` = "perf2_count";

This would have the advantage of eliminating the performance issue of performing a count(*) and would only be executed when data changes in table perf2