title: Lucene Index upgrading from version 4.6 to 8.0.0
body: <p>I am trying to upgrade Lucene index from 4.6 to 8.0.0. When I'm trying to upgrade tool using:</p>
  
  <pre><code>java -cp lucene-core.jar:lucene-backward-codecs.jar \
   org.apache.lucene.index.IndexUpgrader -delete-prior-commits  \
  /scratch/***/workspaces/trunk/****/indexes/4.6/
  </code></pre>
  
  <p>Script is working fine from <code>4.6</code> to <code>5.5.5</code>, <code>5.5.5</code> to <code>6.6.6</code>, <code>6.6.6</code> to <code>7.7.2</code>. But When I am trying to upgrade from <code>7.7.2</code> to <code>8.0.0</code> it is throwing error as below.</p>
  
  <pre><code>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.&lt;init&gt;(IndexWriter.java:846)
      at org.apache.lucene.index.IndexUpgrader.upgrade(IndexUpgrader.java:167)
      at org.apache.lucene.index.IndexUpgrader.main(IndexUpgrader.java:78)
  </code></pre>
  
  <hr>
  
  <p>We want to upgrade from <code>4.6</code> to <code>8.0.0</code>.  Till <code>7.7.2</code> it is upgrading without any issues, but when I'm using for Lucene version <code>7.7.2</code> in my code indexing is working fine. But Lucene <code>8.0.0</code> is not working.</p>
  
  <p>Please help me in upgrading <code>8.0.0</code></p>