Why does MySQL use twice the memory of comparable tools?
Some background first. Our setup is MySQL plus three downstream services, seven figures of daily requests, peaking around nine in the evening.
# Load test: do not jump straight to the max concurrency. # Ramp it up, otherwise you miss the knee. for c in 50 100 200 400 800; do wrk -t8 -c$c -d60s --latency http://127.0.0.1:8080/api/feed sleep 20 done
Worth noting: the official docs do cover this, just in a very inconspicuous spot. I only found it reading the source comments, where the author explains the reasoning — roughly "so that it degrades into predictable behaviour in extreme cases".
One last trap: in container environments remember to adjust the memory-related parameters in step. Otherwise the host limit and the process expectation disagree, and the symptom is intermittent, unreproducible failure.
On trade-offs, my view is this: if nobody on the team owns this area long-term, do not introduce a second mechanism. With two coexistence you first have to work out which one is even in play when things break, and that costs far more than the performance you saved.
The first thing was to collapse the variables. We were changing config and upgrading the version at the same time, and afterwards nobody could say which change caused what. We rolled back to moving one variable at a time, re-ran three times, and only then did the curve settle. Tedious, but not skippable.