https://useinov.com/tags/cache/ Recent content in Cache on Murat Useinov Hugo en-us Tue, 07 Feb 2017 21:30:00 +0300 https://useinov.com/posts/2017/cache-stampede/ Tue, 07 Feb 2017 21:30:00 +0300 https://useinov.com/posts/2017/cache-stampede/ <p>Cache hit rate 98 percent. The database still fell over. Both facts are true, and the second one does not care about the first.</p> <p>What happened. One key holds the result of a heavy query for the main page. TTL one minute. At some second the key expires. In that second a few hundred requests all get a miss, and all of them go to recompute the same heavy query. Redis is fine. MySQL is not. This is a cache stampede, and hit rate will not warn you, because hit rate is an average. The stampede lives in the worst second.</p>