Re: Pre-approval request for dpkg sync() changes for squeeze

[Jonathan Nieder <jrnieder@gmail.com>]

Guillem Jover wrote:

>   1) Switch back from sync() to fsync() before rename() (while keeping
>      the sync() code around for the benefit of other distributions
>      that might not want to switch just yet). So to avoid unrelated
>      I/O when there's background work being done for example. This
>      hack also only works on Linux where sync() is synchronous, so
>      it would unify that code path for all dpkg supported platforms.
>
>      Bug: #588339

Will there be a NEWS.Debian.gz entry for this?  I fear that the
performance degradation would be unacceptable to some people (using
ext4, for example).

>   2) Add a new --force-unsafe-io to disable those fsync() for people
>      using certain file systems where the only option is to choose
>      between reliability or acceptable performance.

dpkg uses the "rename trick" in all the cases this applies to, right?
If so, a certain degree of reliability is guaranteed in precisely
those file systems where fsync() is slow.

What risks remain with --force-unsafe-io on those filesystems?

Context: a good part of ext3's popularity comes from its combination
of speed and resiliance to crashing.  To sacrifice one of the two is
sacrificing something dear to some people.