SVNForum.org - Subversion Forum - Blogs http://www.svnforum.org/blog.php SVNForum.org is a Subversion community help and discussion forum for exchanging information and tips with other users of Subversion. en Thu, 17 May 2012 12:38:45 GMT vBulletin 60 http://www.svnforum.org/images/misc/rss.jpg SVNForum.org - Subversion Forum - Blogs http://www.svnforum.org/blog.php Is svnsync good enough? http://www.svnforum.org/entries/8-Is-svnsync-good-enough Mon, 27 Jun 2011 16:13:14 GMT At WANdisco we offer a clustered Subversion solution which provides both Read AND Write access to replicated repositories hosted over multiple nodes.... At WANdisco we offer a clustered Subversion solution which provides both Read AND Write access to replicated repositories hosted over multiple nodes. Our products are already in use within many large enterprise shops, where the value of replicating the repository in this active-active way is obvious. But one of the questions we hear most often is whether synsync and the Write-through proxy can deliver the same benefits as WANdisco without the additional cost of a third party solution?

Obviously enterprise customers who buy our products don't think svnsync is suitable for their needs, but asking this question internally sparked an interesting discussion and, after trying svnsync for myself, it occurred to me that this blog would be a good place to open up the debate and encourage some contributions to the discussion from the Subversion and general developer community.

Below I've presented the 'WANdisco' view of svnsync when compared to WANdisco's solution. The context here is that we're talking about what is appropriate for *enterprise* development shops who are working in a distributed development environment.

Svnsync Pros:
  • Free, no external product cost

  • Improves local read performance at slave/mirror sites

  • Reduces read traffic from WAN


Svnsync Cons:
  • Master/slave model means a single point of failure - If the master is down no-one can write to the repository.

  • No performance improvement on writes (these are simply proxied to the master server)

  • No guarantee of transactional integrity

  • No topology intelligence

  • Can’t build against slave/mirror if process requires master

  • Manual intervention is normally required in the event of network outage and latency

  • Implementation, configuration, and maintenance generally dependent on a specialised resources (the folks that set it up)

  • No optimization of SVN traffic

  • Recovery time and recovery point objectives are greater than zero

  • No dashboard or central administration

  • Requires additional solution or approach for DR, business continuity, fault tolerance

  • Down time for upgrades or routine maintenance

  • Buggy – More than 5 known issues awaiting attention from a Subversion developer

  • Little, if any, ongoing development input from the Subversion development community


So it's clear that svnsync has one major advantage - cost. But there's also a long list of reasons why we think WANdisco's approach to clustered Subversion is superior. What do you think? Have I missed things from the Pro list for svnsync? Is there anything lacking in our product that would make it more enterprise capable? What features are you looking for in a distributed development solution to support the future needs of your business? ]]> mpoole http://www.svnforum.org/entries/8-Is-svnsync-good-enough Subversion 1.7.0 Alpha packages now available! http://www.svnforum.org/entries/6-Subversion-1-7-0-Alpha-packages-now-available! Mon, 13 Jun 2011 23:25:43 GMT Please remember that Subversion 1.7.0 Alpha is for *testing only* do not install this on a production machine. Source code and official site:... Please remember that Subversion 1.7.0 Alpha is for testing only do not install this on a production machine.

Source code and official site: http://subversion.apache.org
Release notes: http://subversion.apache.org/docs/re...notes/1.7.html
Change log: http://svn.apache.org/repos/asf/subv.../trunk/CHANGES

WANdisco have created Subversion 1.7.0 Alpha packages for:
  • CentOS 5

  • RHEL 5


We plan to have Windows and Ubuntu support shortly. Want us to support a platform? Post and let us know: http://www.svnforum.org/forums/56-Ap...-Alpha-Support

You can download subversion 1.7.0 Alpha from here: http://www.wandisco.com/subversion/download/1_7-alpha ]]> mpoole http://www.svnforum.org/entries/6-Subversion-1-7-0-Alpha-packages-now-available! Windows 7: Bogus ERROR_FILE_CORRUPT error http://www.svnforum.org/entries/3-Windows-7-Bogus-ERROR_FILE_CORRUPT-error Thu, 09 Jun 2011 01:32:12 GMT Subversion performs a lot of tricks, on the both client and server, to keep your data safe. Even in the event of a random power failure or bug in... Subversion performs a lot of tricks, on the both client and server, to keep your data safe. Even in the event of a random power failure or bug in the program, Subversion is designed to make sure your data isn't lost. One of the most common tricks Subversion uses is to take advantage of the underlying operating system's "atomic file move" APIs to make sure a file is never half-written to disk. By first writing a temporary file, and then atomically moving that file into the correct location, Subversion can be sure all of the content is written or none of it is; you don't get half-baked data.
The above approach works great, and is portable to a large number of operating systems. It works great, that is, until there is a bug in the underlying operating system. Microsoft has been kind enough to introduce such a bug in Windows 7.
Windows 7 introduces the concept of the "oplock" for locking file access. The APIs which Subversion uses for platform portability have been updated to use oplocks. In previous versions of Windows, if two applications, such as a virus scanner and Subversion, were to attempt to access the same file, one would get an "Access Denied" error, which that application could then notice and use to retry the access later.
Windows 7, in contrast, emits a "File Corrupted" error in this same scenario. Not only does the calling application not know how to handle the error, this error also gets propagated to the operating system. Windows displays a notice to the user in the system tray, and a complete check disk gets scheduled for the next reboot. To an unsuspecting user, this could look like a serious application bug, or even some kind of hardware failure. Scary stuff!



The key thing here, though is that even though Windows reports corruption, and even though it runs a check disk on the next reboot, no corruption has actually occurred. The check disk runs without incident, and the file contents are unmodified, but the buggy API has caused a confused user, and lots of wasted time.

Microsoft has confirmed this bug:

This is a known regression in Windows 7 in the NTFS file system. It occurs when doing a superseding rename over a file that has an atomic oplock on it (atomic oplocks are a new feature in Windows 7). The indexer uses atomic oplocks which is why it helped when you disabled the indexer. Explorer also uses atomic oplocks which is why you are still seeing the issue. When this occurs STATUS_FILE_CORRUPT is incorrectly returned and the volume is marked "dirty" which is a signal to the system that chkdsk needs to be run. No actual corruption has occurred.
Although this is a bug in Windows itself, there are a few workarounds you can try. Disabling the indexing service, as well as anti-virus scanners will decrease the chance of encountering this error. Subversion 1.7, with the next generation working copy library, will remove many of the scenarios where Subversion needs to do the "atomic rename" trick. But ultimately, the fix will have to come from Microsoft, so I encourage you to use whatever means you have to lobby Microsoft to fix the problem and issue a hot fix.

You can track the status of the bug, via Microsoft's TechNet forums here:
http://social.technet.microsoft.com/...2-bc39e0585148
You can visit the Subversion issue which tracks this bug here:
http://subversion.tigris.org/issues/...ug.cgi?id=3574

UPDATE: Microsoft has released a hot fix for the issue, and indicated that it will included in Windows 7 Service Pack 1. ]]> mpoole http://www.svnforum.org/entries/3-Windows-7-Bogus-ERROR_FILE_CORRUPT-error Subversion 1.6.17 packages available for Mac OS X http://www.svnforum.org/entries/1-Subversion-1-6-17-packages-available-for-Mac-OS-X Sun, 05 Jun 2011 05:53:44 GMT WANdisco have now released Subversion packages for Mac OS X 10.5 and 10.6 Click here to Download Subversion for Mac OS X... WANdisco have now released Subversion packages for Mac OS X 10.5 and 10.6

Click here to Download Subversion for Mac OS X ]]> mpoole http://www.svnforum.org/entries/1-Subversion-1-6-17-packages-available-for-Mac-OS-X