The Chandler Project Blog

Chandler’s repository is intended to store a lot of data that one cannot afford to lose. It should come as no surprise that doing regular backups is strongly recommended. There are a few repository APIs, currently accessible from Chandler’s “Test” menu or from Chandler’s --restore command line option, that make it possible to backup and later restore a repository’s files.

Chandler’s repository is backed by a Berkeley DB environment, a set of files store in a directory called __repository__, itself stored in a somewhat obscure location described here.
This directory contains three kinds of files:

• Berkeley DB environment files: these files are specific to a given machine and are necessary for Berkeley DB to function. They contain no Chandler information, can be re-created at will with no loss of data and are not backed up.
• Berkeley DB transactional log files: these are specific to a given hardware architecture and contain one or more recent transactions. They can contain Chandler data and are backed up. Before a backup is made, the repository is checkpointed, all but the latest log file are flushed into the database files.
• Berkeley DB database files: these are the files with the actual Chandler repository data. Backing them up goes a long way in preventing catastrophic data loss.

When making a backup, the repository’s backup() method will look for a non-existent sibling to the dbHome directory path given to it for storing the backed up files. This new directory may later be used with the repository’s open() method to restore repository files from.

Once a backup is completed the directory where it was made is never written into again. Instead, a restore is done by copying the backup into the dbHome directory argument passed to the open() method, deleting and replacing its content with the files files from the backup.

A backed up repository’s files may be copied and used on another machine. If the target machine’s CPU endianness is not the same as the source machine’s – for example, when going to a PowerPC Macintosh from a Wintel PC – the log files should be deleted first.

This entry was posted on Monday, January 23rd, 2006 at 2:05 pm and is filed under chandlerdb. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.