Monthly Archives: June 2011

Auto-incremented fields in apache’s derby

Unlike MySQL and other SQL dialects, apache derby doesn’t support the AUTO_INCREMENT keyword. To create an auto incremented filed in derby, you can use The value of id is now incremented automagically on every insert. You don’t have to specify it manually in the insert command For instruction on how to create auto incremented fields in other SQL dialects, have… Read more »

Converting an ext3 partition to ext4

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Mounting an ext3 partition using ext4 fs drivers will usually speed-up your filesystem without actually changing the on-disk structures. Therefore it’s possible to revert to the ext3 driver without any problem. This allows you to easily benefit from delayed allocation (delalloc) and multi-block allocation (mballoc). Further performance enhancements are possible if you do change the on-disk structure, e.g. by using… Read more »

Bootstrapping a Fedora 15 rootserver

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In certain situations where you don’t have physical access to your server it can be quite helpful to know how to install a new os without physical media like CD/DVD/USB or pxe. This brief example shows you, how to bootstrap a rootserver (that of course already has a linux os installed that you can access through ssh) to install Fedora… Read more »

Free reserved space on ext4 partitions (or change reserved block percentage)

By default, 5% of a new ext2/3/4 partition will be reserved for important root processes and for fs performance reasons. However, there may be sound reasons to lower that percentage or even disable it completely (non-root partition, data-only storage, huge files, ext4 etc.). Let me quote Linux filesystem guru Ted Ts’o on this: If you set the reserved block count… Read more »