We've been using Solr a bit now for a year or so, 4.6 is the oldest version of Solr we've deployed. We're currently working through the process we'll use to upgrade to 5.1, an upgrade we need for the new facet.stats capabilities.
Reading the Major Changes document, it indicates that there is no longer support for Lucene/Solr 3.x and earlier indexes. It also indicates that you should use the IndexUpgrader included with Solr 4.10 if you're unsure. We've only ever deployed 4.6, and 4.9 Solr installations. Am I safe to assume that we can skip the optimize step and just upgrade to Solr 5.1, perhaps optimizing after we've done that? Thanks, Craig Longman C++ Developer This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, notify the sender immediately by return email and delete the message and any attachments from your system.