There is a showstopping bug with the UIMA processor and using atomic updates in Solr.
I am using the UIMA processor to populate multivalued fields upon indexing. When I later use atomic updates to update a document, all UIMA populated multivalued fields have only one value, the others are gone!
1. Use the org.apache.solr.uima.processor.UIMAUpdateRequestProcessorFactory to populate a multivalued field during the indexing of a document.
2. Use Solr atomic updates (http://yonik.com/solr/atomic-updates/) to set a different field of the document to a new value and commit
3. Any multivalued fields created by the UIMAUpdateRequestProcessorFactory now only have one value.