as of Activiti 5.7, HSQL is not among the list of supported databases. As our unit tests are executed against HSQL, we ported the H2 schema to work with HSQL 2.2.x (basically, the VARCHAR columns in activiti.h2.create.cycle.sql need to be extended with length constraints). Is there any interest to get this into the official Activiti distribution for one of the next releases?
H2 is kind of the 'successor' to HSQLDB, so I do not know if there is real interest in adding it (you might think of switching from hsqldb to h2 ;-)). On the other hand, it does not hurt either but since hsqldb is not a real full scale production db, I'm inclined to say no (but I'm not an official teammember)
We have also our tests with HSQLDB and would like to use activiti with HSQLDB. Are there any plans to get activiti with HSQLDB running? I would be very glad to hear a statement from an official teammember.
I would like to chime in and request hsqldb support too.
We use Oracle as our production server, we have some complex queries which are written in native oracle SQL and H2's compatibility with oracle dialect is lower than HSQLDB's. This forces us to actually use both databases for our tests which can become quite confusing. Until H2 oracle dialect support becomes as good as HSQLDB's I don't think HSQLDB support can easily be dropped. H2 has improvments planned as prority 2 for v1.4 but this doesn't seem to be anytime soon.