Question

Simple question, when should one not use MySQL?

There are two facets to my curiosity:

1. When to avoid MySQL in particular?
2. When to not use relational databases in general?

I wanted to be sure of my choice of MySQL (with PHP on Apache) as my employer was insistent on using something that’s not free or open-source but I insisted otherwise. So I just want to be sure.

Answer 1

1. When to avoid MySQL in particular?

When concurrent database sessions are both modifying and querying the database.

MySQL is fine for read-only or read-mostly scenarios (it is no accident that MySQL is frequently used for Web), but more advanced multi-version concurrency control capabilities of Oracle, MS SQL Server, PostgreSQL or even Firebird/Interbase can often handle read-write workloads not just with better performance but with better correctness as well (i.e. they are better at avoiding various concurrency artifacts that may endanger data consistency).

Even traditional “locking” databases such as DB2 or Sybase are likely to handle read-write workloads better than MySQL.

2. When to not use relational databases in general?

In short: when your data is not relational (i.e. it does not fit well in the paradigm of entities, attributes and relationships).

That being said, many modern DBMSes have capabilities outside traditional relational model, such as ability to “understand” hierarchical structure of XML. So even unstructured data that would not normally be stored in the relational DB (or at best would be stored in a BLOB) is no longer necessarily off-limits.