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Full Discussion: Rescheduling perl script using at command
Top Forums Shell Programming and Scripting Rescheduling perl script using at command Post 302232111 by Smiling Dragon on Wednesday 3rd of September 2008 11:59:09 PM
Old 09-04-2008
Quote:
Originally Posted by DILEEP410
fine.But my question is if i go with your way of letting the script sleep for 1800 seconds, the entire code remains in memory for 30 minutes,right?
But if i reschedule it the memory will be free for 30 minutes.

Since the server is supposed to run a lot of cron jobs may be simultaneously,is better to think from memory perspective.

Please correct me if am wrong,because am not an expert in this!
It's an interesting and valid point, as it's an interpreted script, you'd have the perl engine + any variables etc declared sitting about in memory wheras an 'at' invocation would clear out and leave the memory free until it's needed. I'm of the same school of thought that if we don't need to use RAM, we shouldn't.

But, there are some things to consider:
  • Your average perl binary is pretty small as far as memory footprints go
  • Modern unix systems typically don't have the kind of memory issues we used to have, physical chip ram is still precious but swap space on disk is usually rather copious.
  • CPU time is still precious, to start a new perl interpreter up is considerably more expensive on CPU than just running a sleep (to all intents and purposes, 0% cpu used) for 30 mins.
  • The operational risk _could_ be greater using 'at', this really depends on how the job works though. If you run this thing and it's waiting on some condition to complete before it carries on, could someone make the mistake of seeing it's finished running and thinking that means it's done? They might either run it again (resulting in two 'at' jobs scheduled) or assume it's fully complete.
Smilie
 

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LEARN ABOUT CENTOS

service

service(8)						      System Manager's Manual							service(8)

NAME

       service - run a System V init script

SYNOPSIS

       service SCRIPT COMMAND [OPTIONS]

       service --status-all

       service --help | -h | --version

DESCRIPTION

       service runs a System V init script in as predictable environment as possible, removing most environment variables and with current working
       directory set to /.

       The SCRIPT parameter specifies a System V init script, located in /etc/init.d/SCRIPT.  The  supported  values  of  COMMAND  depend  on  the
       invoked	script,  service  passes  COMMAND and OPTIONS it to the init script unmodified.  All scripts should support at least the start and
       stop commands.  As a special case, if COMMAND is --full-restart, the script is run twice, first with the stop command, then with the  start
       command.

       service --status-all runs all init scripts, in alphabetical order, with the status command.

       If the init script file does not exist, the script tries to use legacy actions.	If there is no suitable legacy action found and COMMAND is
       one of actions specified in LSB Core Specification, input is redirected to the systemctl.  Otherwise the command fails with return code 2.

FILES

       /etc/init.d
	      The directory containing System V init scripts.

ENVIRONMENT

       LANG, TERM
	      The only environment variables passed to the init scripts.

SEE ALSO

       chkconfig(8), ntsysv(8), systemd(1), systemctl(8), systemd.service(5)

								     Jan 2006								service(8)
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