postpone compression while battery operated

Compression :
- increases disk input/output (not just a renaming of the file name)
- increases CPU usage
- increases memory usage

All the above consequences of compression increase the energy consumption and thus decrease the battery lifetime.

I propose to postpone the compression to the next cron cycle if the computer operates on battery. The rotation would still happen whether or not the computer operates on battery.

When the computer operates on main power, the logrotate instance which is launched by the cron job would search for older rotated files which couldn't be compressed up to now and compress them.

This "battery saver" behaviour doesn't need any new option into the /etc/logrotate.* files. It would be silent for the end user and all files would be compressed as expected if the latest cron job ran on main power.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: logrotate 3.7.8-6ubuntu3.1
ProcVersionSignature: Ubuntu 2.6.38-11.50-generic 2.6.38.8
Uname: Linux 2.6.38-11-generic x86_64
Architecture: amd64
Date: Sat Oct 15 11:47:29 2011
InstallationMedia: Lubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427)
ProcEnviron:
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: logrotate
UpgradeStatus: No upgrade log present (probably fresh install)