This keeps some details of jobs in cupsd's mind (well, it keeps the c12345, c12346, and so on, files in the CUPS spool directory, which does a similar job as the old-fashioned BSD-LPD control files). This is set to “Yes” as a default.

This keeps the job files themselves in cupsd's mind (it keeps the d12345, d12346, etc., files in the CUPS spool directory). This is set to “No” as the CUPS default.

This directive controls the maximum number of jobs that are kept in memory. Once the number of jobs reaches the limit, the oldest completed job is automatically purged from the system to make room for the new one. If all of the known jobs are still pending or active, then the new job will be rejected. Setting the maximum to 0 disables this functionality. The default setting is 0.