MySQL Reference Manual :: 14.4.5 Things We Need to Fix for BDB

It's very slow to open many BDB tables at the same time. If you are going to use BDB tables, you should not have a very large table cache (for example, with a size larger than 256) and you should use the --no-auto-rehash option when you use the mysql client. We plan to partly fix this in 4.0.

SHOW TABLE STATUS doesn't yet provide very much information for BDB tables.

Optimize performance.

Change to not use page locks at all for table scanning operations.