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Full Discussion: Cron usage
Operating Systems HP-UX Cron usage Post 302323879 by vbe on Tuesday 9th of June 2009 09:15:14 AM
Old 06-09-2009
Jim pointed out what is the main concern of having plenty jobs scheduled and tansactionnal users at the same time: users working in interractive mode or submiting their jobs can flood the system at some periods when heavy scheduled batches are running...
I used to take care of a system with 3 crontabs running (root for backups policy, oracle for stop/export/start DB) and oper (operational production)
oper had around 200 plannified jobs with some having to be run and finish at given date and time (monthly paiment etc...).
If you add the comments in the file , you realise its about 500 lines long...
Although I was not in charge of the production, I was the one blammed when performance issue occured, which ment having the desagrable task of findinf culprits and killing them so production can continue...

And Jim's comment is to be seriously taken in account:
With already approx 200 lines - you can guess the hard work sorting the different lines that look the same but not quite to match with rules such as "on the second monday of the month" and "every 10 of each month" etc...

I once had the bad surprise of a user sending printing request on a friday afernoon and not seeing his printout strated again and again... then gave up and left for the weekend.
It just happened on the weekend where more than 60 heavy jobs were to run.
I was called out of bed VERY early morning sunday because of a non responsive machine...
At that point all I could do at the console was a reboot ( or was it "turn off the power"?)...
 

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queuedefs(4)							   File Formats 						      queuedefs(4)

NAME
queuedefs - queue description file for at, batch, and cron SYNOPSIS
/etc/cron.d/queuedefs DESCRIPTION
The queuedefs file describes the characteristics of the queues managed by cron(1M). Each non-comment line in this file describes one queue. The format of the lines are as follows: q.[njobj][nicen][nwaitw] The fields in this line are: q The name of the queue. a is the default queue for jobs started by at(1); b is the default queue for jobs started by batch (see at(1)); c is the default queue for jobs run from a crontab(1) file. njob The maximum number of jobs that can be run simultaneously in that queue; if more than njob jobs are ready to run, only the first njob jobs will be run, and the others will be run as jobs that are currently running terminate. The default value is 100. nice The nice(1) value to give to all jobs in that queue that are not run with a user ID of super-user. The default value is 2. nwait The number of seconds to wait before rescheduling a job that was deferred because more than njob jobs were running in that job's queue, or because the system-wide limit of jobs executing has been reached. The default value is 60. Lines beginning with # are comments, and are ignored. EXAMPLES
Example 1: A sample file. # # a.4j1n b.2j2n90w This file specifies that the a queue, for at jobs, can have up to 4 jobs running simultaneously; those jobs will be run with a nice value of 1. As no nwait value was given, if a job cannot be run because too many other jobs are running cron will wait 60 seconds before trying again to run it. The b queue, for batch(1) jobs, can have up to 2 jobs running simultaneously; those jobs will be run with a nice(1) value of 2. If a job cannot be run because too many other jobs are running, cron(1M) will wait 90 seconds before trying again to run it. All other queues can have up to 100 jobs running simultaneously; they will be run with a nice value of 2, and if a job cannot be run because too many other jobs are running cron will wait 60 seconds before trying again to run it. FILES
/etc/cron.d/queuedefs queue description file for at, batch, and cron. SEE ALSO
at(1), crontab(1), nice(1), cron(1M) SunOS 5.10 1 Mar 1994 queuedefs(4)
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