Hit ratio and what it hides
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
read hit ratio correctly.
Planned topics
- Hit ratio = hits / (hits + misses). Aim depends on cost of a miss, not a magic number.
- A high ratio can hide a few very expensive misses or a flood of tiny cheap hits.
- Look at it per cache and per key group, plus miss latency and load on the database.
- A cold start has a 0% ratio; measure after warm-up.
- A hit ratio says nothing about stale data served.
Draft outline details
Demonstration
two caches both at 90%: one saves 1 ms per hit, the other saves 800 ms; the second is worth far more.
Check your understanding
Does a 99% hit ratio prove the cache is correct?
Show answer
No; it can be serving stale data.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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