で、MroongaはDBエンジンとして奉職しているのかというと。

調べてみよう。

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+
| Engine             | Support | Comment                                                        +--------------------+---------+----------------------------------------------------------------
  MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      |
  MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          |
  CSV                | YES     | CSV storage engine                                             |
  BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) |
  MyISAM             | YES     | MyISAM storage engine                                          |
  InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     |
  mroonga            | YES     | CJK-ready fulltext search, column store                        |
  FEDERATED          | NO      | Federated MySQL storage engine                                 |
  PERFORMANCE_SCHEMA | YES     | Performance Schema                                             |
  ARCHIVE            | YES     | Archive storage engine                                         |
+--------------------+---------+----------------------------------------------------------------
 10 rows in set (0.00 sec)

ちゃんといるね。