Yodel again! On Wednesday 02 March 2011 17.02:11 Marius Vollmer wrote: > It shows a speed up between factor six and two in our environment (ext4 > on a slowish flash drive) . I am not sure whether messing with the > fundamentals of dpkg is worth a factor of two in performance
To not be all negative: read the recent discussion about fsync() and other
stuff in dpkg (I'm not sure where the discussion happened exactly; it was
about dpkg becoming extremely slow in some use cases on modern filesystems
like btrfs and was a short time before the release. Since then, there is an
option for dpkg:
unsafe-io: Do not perform safe I/O operations when
unpacking. Currently this implies not performing file
system syncs before file renames, which is known to cause
substantial performance degradation on some file systems,
unfortunately the ones that require the safe I/O on the
first place due to their unreliable behaviour causing
zero-length files on abrupt system crashes.
Note: For ext4, the main offender, consider using instead
the mount option nodelalloc, which will fix both the per‐
formance degradation and the data safety issues, the lat‐
ter by making the file system not produce zero-length
files on abrupt system crashes with any software not
doing syncs before atomic renames.
Warning: Using this option might improve performance at
the cost of losing data, use with care.
So you should compare against dpkg with unsafe-io. Very slightly pre-dating
this: I often (on btrfs, and when I'm inside development chroots that don't
matter much) end up wrapping aptitude/apt-get/dpkg with eatmydata and get
the same benefits. But the tool really deserves its name: a hard reboot
directly after a package installation will leave a mess behind... (I could
so far avoid this; I recently had a zero-length initrd after a kernel
upgrade that *might* have been related. OTOH I did a clean shutdown there so
it shouldn't have happened...)
Yet another point, for the future: I *think* that btrfs is building an
interface so applications can directly access btrfs transactions. Which
would allow to do package upgrades in a btrfs transaction, and since (again,
I *think* so, I'm not sure) can even be ended without forcing an immediate
sync (the result is more like a barrier than a sync), this would be a fine
way to deal with the situation. At the cost that it's btrfs specific.
cheers
-- vbi
--
BOFH excuse #233:
TCP/IP UDP alarm threshold is set too low.
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