I forgot about that list (saw it some time ago). It was good to have a good look at it again. But in the end, the full list is not that interesting if some other high-profile jBPM project/product, the SOA Platform, already made a choice.
Correct?
for development, i want in-process, in-memory db. i never got that easily working with other db's then hqldb.
for the matrix, we should focus on the DB's that the SOA platform supports (assuming that includes what the community wants)
Also important is the availability of a dialect maintained by the Hibernate project. Of the database engines listed in Thomas' reference, only the following have a dialect available.
* Apache Derby
* HSQLDB
* H2
* Mckoi
Derby isn't that tiny or fast compared to HSQLDB or H2. Reading Mckoi, their website says that the latest release happened in... August 2004.