As mentioned in the section called “Berkeley DB”, a Berkeley DB repository can sometimes be left in frozen state if not closed properly. When this happens, an administrator needs to rewind the database back into a consistent state.

In order to protect the data in your repository, Berkeley DB uses a locking mechanism. This mechanism ensures that portions of the database are not simultaneously modified by multiple database accessors, and that each process sees the data in the correct state when that data is being read from the database. When a process needs to change something in the database, it first checks for the existence of a lock on the target data. If the data is not locked, the process locks the data, makes the change it wants to make, and then unlocks the data. Other processes are forced to wait until that lock is removed before they are permitted to continue accessing that section of the database.

In the course of using your Subversion repository, fatal errors (such as running out of disk space or available memory) or interruptions can prevent a process from having the chance to remove the locks it has placed in the database. The result is that the back-end database system gets “wedged”. When this happens, any attempts to access the repository hang indefinitely (since each new accessor is waiting for a lock to go away—which isn't going to happen).

First, if this happens to your repository, don't panic. The Berkeley DB filesystem takes advantage of database transactions and checkpoints and pre-write journaling to ensure that only the most catastrophic of events ^[17] can permanently destroy a database environment. A sufficiently paranoid repository administrator will be making off-site backups of the repository data in some fashion, but don't call your system administrator to restore a backup tape just yet.

Secondly, use the following recipe to attempt to “unwedge” your repository:

This procedure fixes almost every case of repository lock-up. Make sure that you run this command as the user that owns and manages the database, not just as root. Part of the recovery process might involve recreating from scratch various database files (shared memory regions, for example). Recovering as root will create those files such that they are owned by root, which means that even after you restore connectivity to your repository, regular users will be unable to access it.

If the previous procedure, for some reason, does not successfully unwedge your repository, you should do two things. First, move your broken repository out of the way and restore your latest backup of it. Then, send an email to the Subversion user list (at < [email protected]>) describing your problem in detail. Data integrity is an extremely high priority to the Subversion developers.