> The "problem" with log based filesystems is that they most likely
> do not know the consequences of a write so an fsync on a file may
> require double writing to both the log and the "real" portion of
> the disk. They can also exhibit the problem that an fsync may
> cause all pending writes to require scheduling unless the log is
> constructed on the fly rather than incrementally.
Yes, this double-writing is a problem. Suppose you have your WAL on a
separate drive. You can fsync() WAL with zero head movement. With a
log based file system, you need two head movements, so you have gone
from zero movements to two.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
