Search Results for: select * from where

When the subselect runs faster

A few weeks ago, we had a query optimization request from one of our customer. The query was very simple like:

This column in the table is looks like this:

The table have 549252 rows and of course, there is an index on the col1. MySQL estimated the cardinality of that index as […]

Faster MySQL failover with SELECT mirroring

One of my favorite MySQL configurations for high availability is master-master replication, which is just like normal master-slave replication except that you can fail over in both directions. Aside from MySQL Cluster, which is more special-purpose, this is probably the best general-purpose way to get fast failover and a bunch of other benefits (non-blocking ALTER […]

Using delayed JOIN to optimize count(*) and LIMIT queries

In many Search/Browse applications you would see main (fact) table which contains search fields and dimension tables which contain more information about facts and which need to be joined to get query result. If you’re executing count(*) queries for such result sets MySQL will perform the join even if you use LEFT JOIN so it […]

Profiling MySQL queries from Performance Schema

When optimizing queries and investigating performance issues, MySQL comes with built in support for profiling queries aka SET profiling = 1; . This is already awesome and simple to use, but why the PERFORMANCE_SCHEMA alternative? Because profiling will be removed soon (already deprecated on MySQL 5.6 ad 5.7); the built-in profiling capability can only be enabled per session. This […]