A participant aborts. Abort protocol Aborting TM sends abort to all participants and subordinates. Upon Commit, coordinator asks for vote at which point subordinates report the abort back. Commit when commit processing is done. Indicates that coordinator must abort transaction.
Messages can get out of order causing weird commit conditions.
Client sends async messages during transaction and then commits. The commit message reaches servers that are not yet participants, but who become participants when they get their messages. Accept all new participants until commit. S a sends to S b sends to S c sends to S a . Servers give superior role to first superior they have.