On Wed, Oct 24, 2012 at 03:03:00PM -0700, david@xxxxxxx wrote: > Like what is being described for sqlite, loosing the tail end of the > messages is not a big problem under normal conditions. But there is > a need to be sure that what is there is complete up to the point > where it's lost. > > this is similar in concept to write-ahead-logs done for databases > (without the absolute durability requirement) If that's what you require, and you are using ext3/4, usng data journalling might meet your requirements. It's something you can enable on a per-file basis, via chattr +j; you don't have to force all file systems to use data journaling via the data=journalled mount option. The potential downsides that you may or may not care about for this particular application: (a) This will definitely have a performance impact, especially if you are doing lots of small (less than 4k) writes, since the data blocks will get run through the journal, and will only get written to their final location on disk. (b) You don't get atomicity if the write spans a 4k block boundary. All of the bytes before i_size will be written, so you don't have to worry about "holes"; but the last message written to the log file might be truncated. (c) There will be a performance impact, since the contents of data blocks will be written at least twice (once to the journal, and once to the final location on disk). If you do lots of small, sub-4k writes, the performance might be even worse, since data blocks might be written multiple times to the journal. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
