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Introduction to Troubleshooting Performance/Slow queries

mariadb, mysql, percona

Sveta Smirnova provides a guide for Troubleshooting Performance/Slow queries. Here are some of the questions answered by Sveta Smirnova:

  • I’ve heard that is a bad idea to use select *, what do you recommend?
  • If there is a compound index like index1(emp_id,date), will the following query be able to use index? “select * from table1 where emp_id = 10”
  • Finally, only certain composite indexes were suitable, the column order in the complex index mattered a lot. Why couldn’t the optimizer merge the four individual single column indexes, and why did the order of the columns in the composite index matter?