On 12/18/2016 11:30 AM, Lasse Collin wrote:
There's a bug report about data loss due computer losing power. fsync() or fdatasync() in xz would quite likely have avoided the data loss.https://bugs.debian.org/814089 I considered adding fsync() to xz a long ago (it probably was before 5.0.0). I didn't add it because it had a huge performance impact when compressing many small files, and that downside still exists. gzip and bzip2 don't use fsync(). On the other hand, performance doesn't matter so much if there's a too high chance of data loss.
The chance of data loss is somewhat small. Also, in practice the actual damages can be bounded by regular backups [in the case of bug 814089 above, a USB flash memory drive would have served], and/or by using the option "data=journal" when mounting an ext4 file system. For the truly paranoid, LD_PRELOAD a shared library which intercepts the rename() system call, and apply fsync()/fdatasync(). Keep the existing non-fsync() behavior of the xz app. -- John
