Solr - Merging Indexes

1. Run the command:

java -cp lucene-core-3.4.0.jar:lucene-misc-3.4.0.jar org.apache.lucene.misc.IndexMergeTool ./newindex ./app1/solr/data/index ./app2/solr/data/index

to merge two indexes. (Replace the path with your real path)
2. Put the files in newindex into the index directory of your Solr Home. (solr/collection1/data/index)
For more information, go to Merging Solr Indexes