On 5/30/13 7:17 AM, Andres Freund wrote:
> That argument in contrast I find not very convincing though. What was
> the last incidence of such a system call that did not just error out
> with ENOTSUPP or such?
http://linux.die.net/man/2/posix_fadvise talks about POSIX_FADV_NOREUSE
and POSIX_FADV_WILLNEED being both buggy and quietly mapped to a no-op,
depending on your version. I know there were more examples than just
that one that popped up during the testing of effective_io_concurrency. My starting position has to assume that
posix_fallocatecan have the
same sort of surprising behavior that showed up repeatedly when we were
trying to use posix_fadvise more aggressively.
The way O_SYNC was quietly mapped to O_DSYNC (which isn't the same
thing) was a similar issue, and that's the first one that left me
forever skeptical of Linux kernel claims in this area until they are
explicitly validated: http://lwn.net/Articles/350225/
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com
