Hi all, I'm quite new in DBD. I will give my first steps using DPL features of BDB JE.
I was researching in several NoSql technologies and for example MongoDB has a concept of padding, so when you store an entity it automatically adds extra bytes, this way if you update the entity it can use padding bytes for store new data, avoiding the task of moving whole entity into disk.
No, BDB JE does not add padding. I don't know what the MongoDB optimization is about, but I assume from your description it is to allow overwriting a record on disk when it is updated and its size has grown. This doesn't apply to BDB JE, since it always appends data to the end of a file -- it never overwrites. It uses a no-overwrite, append-only log structured storage system. This is described in the documentation.