I am using Sitecore 8.1 with Mongo and Lucene indexes.
I rebuilt the Reporting Database before - it never took more than 10 hours. This time, my PC has been running it for more than 3 days straight.
So far, the only odd symptom is the presence of this exception:
ERROR Exception in alarm clock event subscriber. Message: Binary stream '0' does not contain a valid BinaryHeader. Possible causes are invalid stream or object version change between serialization and deserialization.
Every single minute. Which needs investigating, but surely does not justify a three-fold increase of rebuild time. Is there anything I can do to gauge the progress of the rebuild, and troubleshoot performance?