We're in the process of choosing a new design for our application (DB change included) and we were considering object databases (specifically db4o).
We've built a benchmark test and surprisingly, so far, all tests point that a Hibernate + MySQL implementation is faster at retrieving than an object database.
Granted, there are a lot of variables depending on how the test was designed and run, the test dataset and so on, however if I'm reading the below results correctly:
http://www.jpab.org/Hibernate/MySQL/server/DataNucleus/DB4O/embedded.html
This also shows a MySQL implementation to be better.
What we would like ton know is what could make object databases slower as opposed to MySQL (bad-practices let's say) and how could one avoid them. And if they are indeed slower, then what are the advantages of such a DB (so far we've mostly been reading about read/write speeds of object dbs as being higher than SQL ones).