MySQL Cluster / OCI Heatwave

[fopinappb]

The adaptative backend criteria (https://github.com/etianen/django-watson/blob/master/watson/backends.py#L463-L469) fails when using a clustered MySQL such as OCI Heatwave.

Explicitly choose Regex one, resolves it (with the performance impact that comes with it).

The issue comes with this line https://github.com/etianen/django-watson/blob/master/watson/backends.py#L369

MyISAM is not available in these solutions - it is not atomic so it cannot be used in a cluster.

I think it would be nice if lack of MyISAM was detected and an alternative approach was used instead: either falling back to regex backend or actually using some full text solution with innodb