from https://github.com/processone/ejabberd/blob/master/src/mod_mam.erl

start(Host, Opts) ->
    case mod_mam_opt:db_type(Opts) of
	mnesia ->
	    ?WARNING_MSG("Mnesia backend for ~ts is not recommended: "
			 "it's limited to 2GB and often gets corrupted "
			 "when reaching this limit. SQL backend is "
			 "recommended. Namely, for small servers SQLite "
			 "is a preferred choice because it's very easy "
			 "to configure.", [?MODULE]);
	_ ->
	    ok
    end,


but

[critical] <0.107.0>@ejabberd_app:start:71 Failed to start ejabberd application: Invalid value of option modules->mod_mam->db_type: unsupported database: sqlite