vtworker hosts long-running processes. It supports a plugin architecture and offers libraries so that you can easily choose tablets to use. Plugins are available for the following types of jobs:
- resharding differ jobs check data integrity during shard splits and joins
- vertical split differ jobs check data integrity during vertical splits and joins
vtworker also lets you easily add other validation procedures. You could do in-tablet integrity checks to verify foreign-key-like relationships or cross-shard integrity checks if, for example, an index table in one keyspace references data in another keyspace.