On 3/25/2016 5:32 PM, Shawn Heisey wrote: > You are correct. Solr (Lucene, actually) only maintains compatibility > with indexes from the previous major version, so 6.x will read 5.x > indexes, but not indexes built by 4.x or earlier.
Further clarification on this specific point. This is your TL;DR warning. It might be more info than you wanted: This compatibility assumes that the underlying data type is still present in the new version. As an example of where this becomes important: Solr's IntField class was deprecated in version 4.8. It had not been prominently featured in Solr example schemas for a VERY long time, though. The "int" type in examples has been TrieIntField as far back as 3.x versions, and possibly longer. If you have an index containing fields built by a 4.x fieldType using IntField, you cannot use that index in 5.x, even though the index *format* is readable by 5.x. The code to access an IntField value from the index was removed from 5.x in accordance with project policy on deprecated code. If you try changing the type in 5.x to TrieIntField, the recommended replacement, that won't work either, because TrieIntField encodes the data on the disk differently than IntField did, and cannot correctly read the data originally written by IntField in the 4.x version. Thanks, Shawn
