Good idea. But I wonder whether calling the trigger each insert will loose any performance.
It's going to affect things slightly but whether it'll be noticable only you can answer by testing.
Another option I sometimes see is set up a replicated slave and run your reports off that instead of the live system, then:
1) it won't bog the live db down
2) it doesn't really matter how many queries you run
3) it doesn't really matter how long they take to run
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