Export Entries (.rdm) causes DB to grow in size

Hi,
I am running 9.9.0.0 and have a SQLite datasource.
It has about 3300 entries and is about 17.MB in size.
So wanted to do and export of all entries, with credentials and master key, for backup purposes.
After I started the export I noticed that the size in the database kept growing, and after it finally finished it was almost 20MB.
Is that growth normal when you do an export? Worried if I do more it will just keep growing.
I know it's not that bit, but more worried about over time.

Thanks
Bill