The internal job ticket for each job contains a field that records the job's arrival stamp.
Unless job priorities dictate otherwise, Switch processes jobs in order of arrival (if there is a matching execution slot). Switch uses the arrival stamp to determine which job arrived first. See scheduling jobs.
An arrival stamp is a signed integer number (in the range that can be represented with 32 bits). It indicates the order in which a job first arrived in a flow, as compared to other jobs. Switch maintains a persistent and global arrival count that gets incremented each time a new arrival stamp is handed out. Thus a higher number indicates a more recent arrival.
Several jobs may have the same arrival stamp. This happens when multiple jobs are generated from the same original job, or when for some reason no arrival stamp was assigned to a job.
Switch assigns a new arrival stamp to a job when it first detects the job in a folder or submit hierarchy, or when a producer (such as FTP receive or Mail receive) first injects the job into a flow. A job's arrival stamp is not affected while the job is moving along a flow. Results generated for a job (such as a preflight report, or a duplicate of the job) retain the original job's arrival stamp.
In certain situations a job's arrival stamp needs to be refreshed (that is, assigned a fresh stamp) so that the job is not unduly processed before other jobs. For example, a Checkpoint refreshes the arrival stamp when moving a job along one of its outgoing connections.