The only "safe" way to use SignatureUpdateProcessorFactory for de-duplication in SolrCloud is to define the signatureField to be the same as the unique key field – ie: let SignatureUpdateProcessorFactory generate the 'id' for each document
We should add a note about this to the ref-guide ASAP for inclusion in the next release
There are currently no "cloud" based tests of SignatureUpdateProcessorFactory showing that even this usage works
We should add a basic test of this usage ASAP to future-proof against it breaking
Major