Each BDB table stores in its .db file the path to the file as it was created. This is done to enable detection of locks in a multi-user environment that supports symlinks. As a consequence of this, it is not possible to move BDB table files from one database directory to another.

When making backups of BDB tables, you must either use mysqldump or else make a backup that includes the files for each BDB table (the .frm and .db files) as well as the BDB log files. The BDB storage engine stores unfinished transactions in its log files and requires them to be present when mysqld starts. The BDB logs are the files in the data directory with names of the form log.NNNNNNNNNN (ten digits).

If a column that permits NULL values has a unique index, only a single NULL value is permitted. This differs from other storage engines, which permit multiple NULL values in unique indexes.