We are planning to migrate from Solr 4.10.4 to 5.5.2 in the next couple of months. We do not use SolrCloud.
When doing initial testing in our dev and qa environments we ran into cases where we got errors for fields that had docvalues newly enabled, but not re-indexed. Mixed docvalues/non-docvalues was possible due to ongoing indexing. Specifically, when we tried to sort or facet we sometimes got errors like: “IllegalStateException: unexpected docvalues type NONE for field 'id' (expected=SORTED). Use UninvertingReader or index with docvalues.” Id is a string field with docValues=true. This did not always consistently happen, but any occurrence of this is troublesome. My reading of tickets like https://issues.apache.org/jira/browse/SOLR-7190 is that when docvalues is not fully available, Solr will fall back to the UninvertingReader. But the error message seems to indicate this is not done automatically for a sort. In general, is there a way to migrate existing indexes (we have petabytes of data) by enabling docvalues and incrementally re-indexing? We expect the latter would take a month using an atomic update process. Could this be an artifact of having old 4.x indexes, and it would be wiser to first migrate the indexes to 5.x format before enabling docvalues? (We expect that would also take us a month using incremental optimize.) Can someone clarify what migration paths to docvalues are likely to succeed? Thanks! -Ronald Wood.
