I did see that discussion, but it seems to contradict with the claim that the database operations are transactional.
So, my follow up is: If I unplug the network cable between svn-commiter and filesystem, will the repository be corrupt? If yes, then the underlying database is not atomic and therefore not transactional. If no, then the server can take a snapshot at any point in time, and the snapshot is guaranteed to be consistent. -- -Justin -----Original Message----- From: Les Mikesell [mailto:lesmikes...@gmail.com] Sent: Monday, August 02, 2010 12:30 PM To: users@subversion.apache.org Subject: Re: Support for filesystem snapshots (?) On 8/2/2010 11:17 AM, Stefan Sperling wrote: > On Mon, Aug 02, 2010 at 11:38:30AM -0400, Vallon, Justin wrote: >> In the svn book, >> http://svnbook.red-bean.com/en/1.1/ch05s03.html#svn-ch-5-sect-3.6 on >> "Repository Backup" describes some backup methods - hot copy, etc. Given >> that enterprise-level filesystems generally support filesystem snapshots, >> what is SVN's position on whether such snapshots are sufficient for backups? >> >> Suppose our criteria is that we unplug the network cable between the writer >> (svn commit) and the filesystem. If unplugging the network cable could >> yield a repository that is corrupt, then doesn't that mean that there are >> failure modes where the repository is corrupted? If a filesystem insures >> that the snapshots behave in this way (as if you disconnect the network >> cable, make an instant copy, then reconnect), it would seem to imply that >> these volume-level snapshots would result in a consistent view. If the >> snapshots are not consistent, then atomicity is not being insured (somewhere >> between application, client o/s, server o/s, disk controller, media). >> >> My follow up is whether the svn book could include a word about whether it >> blesses (or not) this form of backup? > > By chance, this very topic was discussed earlier today. > See http://svn.haxx.se/users/archive-2010-08/0019.shtml > > Quote: > "Use 'svnadmin hotcopy' to create a copy of a repository that is consistent > from Subversion's point of view. There is no other repository copying > tool that can guarantee a consistent repository snapshot." > > This holds true for filesystem-level snapshots. > The atomicity of Subversion's commits only exists from the application's > point of view. Are there any svnadmin commands that could quiesce/lock the repository in a consistent state for the duration of a filesystem snapshot - or if not, could that be added as an enhancement? -- Les Mikesell lesmikes...@gmail.com
