[tahoe-lafs-trac-stream] [tahoe-lafs] #1937: back up the content of a file even if the content changes without changing mtime

[tahoe-lafs]

#1937: back up the content of a file even if the content changes without changing
mtime
-------------------------+-------------------------------------------------
     Reporter:  zooko    |      Owner:
         Type:  defect   |     Status:  new
     Priority:  normal   |  Milestone:  undecided
    Component:  code     |    Version:  1.9.2
   Resolution:           |   Keywords:  tahoe-backup reliability
Launchpad Bug:           |  preservation
-------------------------+-------------------------------------------------

Comment (by zooko):

 Here's a proposed solution which avoids the failure of preservation due to
 the race condition. This solution does not address the problem due to
 timestamps getting reset, e.g. by {{{touch -t}}} or by the system clock
 getting moved.

 Let {{{G}}} be the local filesystem's worst-case Granularity in seconds
 times some fudge factor, such as {{{2}}}. So if the filesystem is FAT, let
 {{{G=4}}}, if the filesystem is ext4, let {{{G=0.002}}}, if the filesystem
 is NTFS, let {{{G=0.004}}}, else let {{{G=2}}}.

 When {{{tahoe backup}}} examines a file, if the file's current {{{mtime}}}
 is within {{{G}}} seconds of the current time, then don't read its
 contents at that time, but instead delay for {{{G}}} seconds and then try
 again.

-- 
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1937#comment:1>
tahoe-lafs <https://tahoe-lafs.org>
secure decentralized storage