A transaction_id is a unique identifier that identifies the present or past transaction. A transaction is made up of one or more sub-transactions. A transaction has one role for the entire lifetime, but the transaction can different values of status as the transaction is processed.

For example, if the user "Installed OpenOffice" and the backend has to:

This is one single transaction with the role install, with 4 different sub-transactions. This allows the user to rollback transactions with selected backends, rather than select sub-transactions which may need complex conflict resolution.

The transaction_id must be of the format /job_identifier_data where the daemon controls all parameters. job is a monotonically updating number and is retained over reboots. identifier is random data used by the daemon to ensure jobs started in parallel cannot race, and also to make a malicious client program harder to write. data can be used for ref-counting in the backend or for any other purpose. It is designed to make the life of a backend writer a little bit easier. An example transaction_id would be /45_dafeca_checkpoint32