In an orchestration-based saga, a centralized transaction coordinator is responsible for coordinating the updates to the databases and for rolling back failed transactions. 

Each microservice communicates with the transaction coordinator to initiate and commit its sub-transactions, and the transaction coordinator is responsible for coordinating the overall saga transaction. 

https://medium.com/@ijayakantha/microservices-the-saga-pattern-for-distributed-transactions-c489d0ac0247