This is concerned with getting all nodes to agree on the outcome of a transaction.
2PC
The application reads and writes data on multiple database nodes which are participants. When the application is ready to commit, the coordinator sends a prepare request to each node asking them if they are ready to commit. If all participants reply yes, then a commit request is sent. Otherwise, an abort request is sent. A participant can only reply yes if all transaction data can be written to disk under all circumstances.