Accidentally I discovered the link to Sanakirja plus in Google:
https://pijul.org/documentation/sanakirja_plus/
But, the link is not shown in https://pijul.org/documentation. Is it on purpose?
So, Sanakirja + was abandonned about a year and a half ago. Since then, Sanakirja has been mostly rewritten, the only remaining part from before being the transaction module, the one in charge of allocating pages in the file, and making everything transactional.