To understand why MySQL is the most widely used database within Zabbix and why Zabbix SIA tends to use MySQL (for main development and ready-to-use appliances) instead of other RDBMS, you need to know some details about the supported databases and the main characteristics directly related to Zabbix.

According to the Zabbix manual at https://www.zabbix.com/documentation/2.4/manual/appendix/performance_tuning, Zabbix SIA has good support for MySQL.

This topic does not offer a comparison to determine which the best database is, but a comparison to understand which database has the best behavior with the Zabbix platform. The difference in approach is important so that you can have an assessment free of any bias, positive or negative, regarding any of the databases supported by Zabbix.

We know that the Zabbix server and the Zabbix proxy natively support five databases: