Lucene Index upgrading from version 4.6 to 8.0.0

Question

I am trying to upgrade Lucene index from 4.6 to 8.0.0. When I'm trying to upgrade tool using:

java -cp lucene-core.jar:lucene-backward-codecs.jar \
 org.apache.lucene.index.IndexUpgrader -delete-prior-commits  \
/scratch/***/workspaces/trunk/****/indexes/4.6/

Script is working fine from 4.6 to 5.5.5, 5.5.5 to 6.6.6, 6.6.6 to 7.7.2. But When I am trying to upgrade from 7.7.2 to 8.0.0 it is throwing error as below.

Exception in thread "main" org.apache.lucene.index.IndexFormatTooOldException: Format version is not supported (resource BufferedChecksumIndexInput(MMapIndexInput(path="/scratch/**/workspaces/trunk/**/indexes/4.6/sd/segments_9"))): This index was initially created with Lucene 6.x while the current version is 8.0.0 and Lucene only supports reading the current and previous major versions.. This version of Lucene only supports indexes created with release 7.0 and later.
    at org.apache.lucene.index.SegmentInfos.readCommit(SegmentInfos.java:318)
    at org.apache.lucene.index.SegmentInfos.readCommit(SegmentInfos.java:289)
    at org.apache.lucene.index.IndexWriter.<init>(IndexWriter.java:846)
    at org.apache.lucene.index.IndexUpgrader.upgrade(IndexUpgrader.java:167)
    at org.apache.lucene.index.IndexUpgrader.main(IndexUpgrader.java:78)

---

We want to upgrade from 4.6 to 8.0.0. Till 7.7.2 it is upgrading without any issues, but when I'm using for Lucene version 7.7.2 in my code indexing is working fine. But Lucene 8.0.0 is not working.

Please help me in upgrading 8.0.0

Answer 1

1. If we are upgrading more than one major version, we must re-index.
2. Multiple major version upgrades have always been discouraged and never guaranteed to work, but now such upgrades are explicitly denied.
3. When we used the IndexUpgrader from Lucene 6, the Lucene version was written into the index. The recorded version was preserved by the upgrader for version 7. When the index was subsequently read by version 8, it complained because the original index was not written by version 7 or later.