WorldServer creates many database objects to represent different elements (projects, tasks, segmented documents, and so on). A set of cleaners deletes these obsolete objects periodically, in a process known as "garbage collection", to reclaim database space.
Some created objects are deleted as soon as they become obsolete, but most are not. There are good reasons for this. For one, deleting objects can be a time consuming procedure that ties up resources. For another, it is not always immediately clear when an object becomes obsolete.
For example, when an asset is translated in the WorldServer Browser Workbench it is segmented into the "Segmented Document" structure. This structure is used internally as long as the corresponding asset does not change. When the asset does change, a new segmented document structure is created and the old one is left in the database, marked for garbage collection.
Garbage collection consists of several cleaners, each of which cleans up a particular area in the WorldServer schema. You can schedule the cleaner tasks separately, if you like.
By default, WorldServer garbage collection starts running every night at 12:45 AM. You can modify cleaner schedules from the page.