Why allow dirty read when it happens network partition in VoltDB?

Question

I am PhD student in Seoul National University. My name is Seokwon Choi. I impressed research paper(Analysis for network partition fault). I hope to present this paper with my lab member at lab seminar time.

However, I read your research paper and your presentation slide. I have one question.

Why the read operation read Y value in VoltDB? Actually replication is fail, so write is fail. Why it update Y value in local storage?

and read operation read value Y that updated locally?

I think read operation should read commit value(written successfully: in this case-> value X).

I try to find VoltDB Document. It can allow dirty read in VoltDB. Why allow dirty read when it happens network partition in VoltDB?

Is there any reason to work like this?

I attached picture of dirty read when network partition

Thank you

Best Regards

From Seokwon Choienter image description here

Answer 1

VoltDB does not allow dirty reads. In your picture, you show a 3-node cluster where 1 node gets partitioned from the other 2 and the single node is a partition master.

Event1: Network partition Event2: Write to minority (and you show that the write fails, which is correct) Event3: Read from minority (and you show a dirty read, which is incorrect).

Event 3 is not possible. The single node that gets partitioned from the other two will shut down its client interface and then crash, never allowing event 3 to happen.

We ran Jepsen tests several years ago and fixed a defect in V6.4 that in some circumstances would allow that dirty read from event#3. See https://aphyr.com/posts/331-jepsen-voltdb-6-3 and https://www.voltdb.com/blog/2016/07/12/voltdb-6-4-passes-official-jepsen-testing/ for the full details on the guarantees from VoltDB, the Jepsen testing we did, and the defects that were fixed in order to pass the test.

Disclosure: I work for VoltDB.