Half edges and ghost vertices repair solutions.

[Alexandr Porunov]

Hello,

I would like to open a thread to talk about problems in eventually consistent databases and their solutions. 

Problems and some solutions are described here:

https://docs.janusgraph.org/latest/eventual-consistency.html

Any ideas are welcome in this thread. 

The biggest problem which I can't solve right now is "half edges". The situation is that sometimes they appear and should be resolved somehow. The biggest problem is that they are hard to be detected.

Till now I can imagine only one solution:

1. Get an edge from the vertex A.

2. Get a connected vertex B from that edge.

3. Retrieve vertex B by id.

4. Search if that retrieved vertex B has an edge which connects to vertex A.

5. If there is no such edge then an edge in vertex A is "half edge" and should be repaired.

As you see this solution is very costly (especially the step 4). Does somebody know any other less costly solutions or any ideas?

To detect "ghost vertices" I found two additional ideas:

1. When we retrieve a ghost vertex it will have 0 keys which may signal a vertex checking.

2. It is possible to use a solution like read_repair_chance. I.e. randomly (with some coefficient) check if the vertex exists in the database.

Again, any ideas are welcome.

Related thread: 

https://groups.google.com/forum/#!topic/janusgraph-users/uxM0uDCwfL0

Best regards,

Alexandr