If the following error occurs when you start mysqld after upgrading, it means that the current version of BDB doesn't support the old log file format:

bdb:  Ignoring log file: .../log.NNNNNNNNNN:
unsupported log version #

In this case, you must delete all BDB logs from your data directory (the files that have names of the form log.NNNNNNNNNN) and restart mysqld. We also recommend that you then use mysqldump --opt to dump your BDB tables, drop the tables, and restore them from the dump file.

If autocommit mode is disabled and you drop a BDB table that is referenced in another transaction, you may get error messages of the following form in your MySQL error log:

001119 23:43:56  bdb:  Missing log fileid entry
001119 23:43:56  bdb:  txn_abort: Log undo failed for LSN:
                       1 3644744: Invalid

This is not fatal, but the fix is not trivial. Avoid dropping BDB tables except while autocommit mode is enabled.