How to change multiplicity of an edge in TitanDb? I've got an edge set to ONE2MANY but need to change it to MULTI.
Not possible.
When an edge is marked as unique - ONE2MANY or MANY2ONE , its raw data (as stored internally by Titan on the backend, for example, HBase) is different than non-unique ones, such as edges marked as MULTI.
So even if you make Titan consider your edges as MULTI ones, it will fail parsing the old ones which were once unique.
Ideally you would like to migrate the old data to the new form, but as far as I am concerned, there is no standard way to do it. The only solution is to re-insert the edges.