Tau Station, The Internal Adventures: DBIx::Class::Row cache (avoid the rabbits!)

Tau Station, "the free-to-play narrative sci-fi MMORPG (TM)", has a nicely complex database. Currently, we have 190 tables with 740 relationships between those tables. DBIx::Class does an amazing job at managing that complexity, since each relationship is simply an accessor on the DBIx::Class::Row object.

However, there is a subtle issue when using those relationship accessors. Using a relationship accessor creates a new Row object and stores it in the calling object. This behavior can easily leads to duplicate DBIC Row objects for a single database row. At best, the duplicates cause wasted resources duplicating the Rows. At worst, they cause update anomalies, since updates done to one Row object are not seen by the duplicate objects.

With a highly-connected schema like we have in Tau Station, trying to handle the object duplication can pretty soon feel like we're trying to handle rabbits in Australia.

In order to avoid this Row duplication, we have developed a cache of DBIC Row objects that is shared within the application. In most cases, this allows us to ensure that we have one DBIC Row object per database row while processing an HTTP request, avoiding those subtle update anomalies.