"C. Michael Pilato" <cmpil...@collab.net> writes: > On 08/08/2012 07:38 AM, Philip Martin wrote: >> I've been asked about using operating system snapshots to make backups >> of live repositories. These could be filesytem snapshots like ZFS or >> FreeBSD's UFS2, or block level snapshots like Linux's LVM, or maybe even >> a Windows shadow copy. The reasons for using snapshots, rather than >> "svnadmin hotcopy", are that it's a better fit with the overall backup >> strategy or that it is faster or requires less disk space or less IO. >> This has also been discussed on the mailing lists, e.g. >> http://svn.haxx.se/users/archive-2012-02/0233.shtml >> As far as I know the snapshot method should work provided there are no >> bugs in Subversion or the snapshot code but it would be good to have >> more confidence that it works. >> >> One of our customers asked about locking the FSFS write-lock file before >> taking the snapshot as this would halt writes and make the repository >> quiescent. It's certainly possible to do it, I wrote a program that >> calls the private API svn_fs_fs__with_write_lock, but calling a private >> API is a hack and I need to lock the rep-cache as well. >> >> So I was wondering whether we should introduce a public API to do this >> properly either at the svn_fs_ or svn_repos_ level. For FSFS this would >> stop writes while allowing reads. A BDB implementation would probably >> stop reads as well. > > This seems reasonable. I can envision the likes of an > svn_fs_freeze()/svn_fs_unfreeze() API pair, with svn_repos_* flavors thereof > for adding hook support.
I had not considered hook support. Would that be pre-freeze and post-unfreeze hooks? Or something (not sure what) to do with the existing hooks? A _freeze/_unfreeze API would work but a callback interface like svn_fs_fs__with_write_lock (_with_freeze or _frozen) means that repository is unfrozen automatically even if the callback fails, so no dangling frozen repositories. It practice it makes little difference since the main user would be svnadmin, or a imilar program, that is short lived and will unfreeze on exit. -- Certified & Supported Apache Subversion Downloads: http://www.wandisco.com/subversion/download
