[cups.development] [RFE] STR #2681: check of snmp status of printer before sending job

[Johannes Meixner]

Hello,

On Jan 22 03:40 Johannes Feigl wrote (shortened):
> if i send an e.g. 10 printjobs to the mashine all of the are store in the
> mashine and they are finished for cups.
> 
> if i now have a problem with the printer, i don't know (from the cups)
> which has not been printed yet and i cannot move the jobs to an other
> printer.
> 
> so it would be usefull, if cups would make a SNMP-check on the printer, of
> the printer is ready to print (no paper jam, or other jobs to perferm)
> before cups is sending the job to the printer.

I do not understand how this should help against loss of jobs.

Assume there is such a check, the printer may be filled up
with printjobs nevertheless because the printer could be
ready to print all the time while the jobs are sent.
But then while it actually prints e.g. the third job,
the printer firmware may crash or there is a memory corruption
in the printer (or a built-in harddisk in the printer dies)
so that all data in the printer would be lost.

On the other hand if the backend would wait for each job
until its last page was actually printed before a subsequent
job is sent to the printer, the printer's throughput would
decrease in particular under high load. In the end such a
"wait-until-actually-printed" could reduce a high performance
printer to something like a small-office/home-office device.

To be really safe against loss of jobs inside printers
I think it is best to use PreserveJobFiles, see
http://www.cups.org/documentation.php/ref-cupsd-conf.html

To avoid misunderstandings:
I don't mean that something like "waitprinter" for a backend
is useless. I only like to point out that there are drawbacks
(not 100% safe against loss of data and/or reduced performance).

Kind Regards
Johannes Meixner
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