[ Mike Hommey ]
> While this is stricly true, there are still two fsync()s occuring on each
> package unpack, making the whole thing still slow when installing many
> packages at a time.
> 
> These happen for /var/lib/dpkg/updates and /var/lib/dpkg/tmp.ci.

[  Raphael Hertzog ]
> This is on purpose.

Can you explain in which situation where --force-unsafe-io is used
that you believe these fsync()s to be an advantage?  I've tried to
come up with such scenarios without any luck so far.

The users of --force-unsafe-io seem to be those that know that if
something go wrong during installation, they scratch everything and
start again, and finishing quickly is more important than handling
power outages.  One example is building live CDs.  Another is
installing the system for the first time.  A third is creating chroots
for testing.  In all these cases any power outage or other system
failure will make one erase everything and start over, and there is no
need for dpkg to keep an consistent state.

I would love my distro upgrade test to become faster and thus hope
also these fsyncs can go away.  I install stable in a chroot,
dist-upgrade to testing, and check the rsult.  If the something go
wrong I remove the chroot and start over, so there is no need for any
sync to disk. :)
-- 
Happy hacking
Petter Reinholdtsen



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