Thanks for reminding. It is originally reported with the default setting. We conducted further tests with other options of anydbm (dbhash, dbm, gdbm), none of them survived crash testing. For the detailed reasoning please refer to an OSDI'14 research paper: https://www.usenix.org/system/files/conference/osdi14/osdi14-paper-pillai.pdf
 This paper discussed vulnerabilities of GDBM implementation in that paper, and these lightweight db implementations have similar problems. We also have tests SQLite, and it is much more robust that we have not found ACID violation yet.

Personally I think it is reasonable to have an SQLite backend, as it is much safer (plus providing thread safety). Just to see what I can do for that.