[Bug 601299] Re: btrfs fsync() is extremely slow

[Phillip Susi]

The debian bug you link to did not actually fix this.  The debian devs
simply dodged the issue by adding a --force-unsafe-io flag to dpkg that
slightly reduces ( but nowhere near eliminates ) the ridiculous number
of syncs dpkg does.  The idea was that debian-installer should use this
flag to speed up installations.  Not only does it not go nearly far
enough during installation, but it does nothing for installing or
upgrading packages on an existing system.


** Changed in: dpkg (Ubuntu)
       Status: Fix Released => Triaged

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https://bugs.launchpad.net/bugs/601299

Title:
  btrfs fsync() is extremely slow

Status in dpkg package in Ubuntu:
  Triaged
Status in dpkg package in Debian:
  Unknown

Bug description:
  Installation and upgrades on btrfs are *extremely* slow.  This is
  because dpkg makes extensive fsync() calls to make sure that a power
  loss in the middle of an operation does not leave the system in a
  broken state.  These calls have a significant performance penalty on
  other filesystems ( such as ext[234] ), but on btrfs, the penalty is
  multiple orders of magnitude.

  As a workaround, you can use the eatmydata package/command around dpkg
  /apt-get to disable the fsync() calls and restore good performance
  during upgrades, at the risk of hosing the system if it crashes.  The
  apt-btrfs-snapshot package will have apt make a snapshot before it
  begins an upgrade so that if things do go wrong, you can at least roll
  back to the snapshot.

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