Introduction
Queries are ubiquitous in the life of every MySQL database administrator or even a database-savvy developer. As we have already stated in some of our previous blog posts, queries are simply tasks composed of smaller tasks. To optimize their performance, we should make those smaller tasks execute quicker or not execute at all. First, we must examine how MySQL performs its queries. We have already covered the basics of what makes queries slow in MySQL and we came down to the fact that we need to profile our queries-the query cache was one of the first things that MySQL looked at, remember?
What Is the Query Cache?
The MySQL query cache, though deprecated in MySQL 5.7 (and removed in 8.0), stores statements that have previously been run in memory: in other words, a query cache usually stores SELECT statements in the memory of a database. Therefore, if we run a query and then run precisely the same query again after a while, the results will be returned faster because they will be retrieved from memory and not from the disk.