Re: disabling syncs ( was: suite wide config options? )
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On 11/01/2011 10:50 PM, Guillem Jover wrote:
> As said before countless times (I think there's even a wontfix bug
> report), I don't want to see an option that disables syncs on the
> database, which has always performed them. There's so much rope
> I'm willing to give to the user. If the user does not value their
> data, or they are using a throw-away filesystem, then yes, kindly
> use something like libeatmydata, or use a saner filesystem...
Why should they use a third party LD_PRELOAD library ( which sudo
disables ) to make dpkg usable? What does keeping it out of dpkg gain?
> For the btrfs case, it seems like there's something to fix in the
> filesystem implementation, those numbers are atrocious. In
> addition (something I've mentioned before too), if btrfs does not
> currently have it, it should get sync_file_range() support. In any
> case the current situation on btrfs means that fsync() is otherwise
> completely unusable (when the filesystem makes it necessary?).
While the performance of syncs on btrfs is horrid and should be
improved, there is nothing sane about continuing to use them when you
know they are entirely pointless. Even on ext4 disabling the syncs
offers a 600% speed up, and if you have a system snapshot that the
boot loader can easily roll back to if the upgrade does not complete
correctly, then all of these database syncs are a complete waste of time.
On a traditional filesystem, going to some length to ensure the system
will still boot after a crash is perfectly reasonable, but in the
presence of snapshots, such effort is entirely wasted, regardless of
whether it is a 600% or a 120,000% performance penalty.
Even if btrfs is eventually improved to to be just as fast as ext4 in
this regard, why should users be forced to suffer through a two hour
long dist-upgrade when it could be done in 20 minutes, and still be safe?
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