I've just upgraded my previous alfresco 50d instance to 201702, and also switched to solr6.
Left the new instance indexing over the weekend, but on morning morning when I checked (after almost 36 hours), it had only indexed perhaps 12% of documents, and from previous experience: (1) the CPU usage is not high enough to indicate it is continuing the indexing (it is indexing new documents, but no the existing/old ones), and (2) 36 hours was more than enough time for solr4 to reindex 90+% of the documents when I upgraded from alfresco 4.2 to 502d.
As example, on the previous alfresco 50d instance, my solr4 indexes were taking up 235GB of disk space, alfresco core had 3880462 current documents, and archive core had 2036546 documents. Currently, the new solr6 index is only taking up 3.5gB of disk space, whilst alfresco core has only 475244 current documents, and archive 432393. Unless solr6 is super-efficient to almost 2 orders of magnitude, I think I have a serious index issue!
I don't see any errors in the solr6.log nor solr-8983-console.log, related to this.
Anybody encountered similar issues? If by the end of the week the indexing hasn't substancially increased in document count, then I will probably have to switch back to solr4.