How to upgrade properly from solr 4.0 to 4.2?

Question

My solr Update extract handler stopped working after upgrading from 4.0 to 4.2

When I upgraded from solr 4.0 to 4.2 suddenly all the file uploads using /update/extract stopped working. I noticed a class was missing.

I've solved this by making by changing solrconfig(from 4.2) with the changes I had in 4.0.

Because of al these problems I'm wondering whats the best way to upgrade from Solr 4.0 to 4.2? (or any other version)

I just copied the new war,dist folder and contrib folder and tought it would be fine but it sure isn't. I know re-indexing is recommended.

Answer 1

Typically when I upgrade between Solr versions, I follow the steps outlined below...

1. Read the entire release notes for the new release. Especially checking the "Upgrading from Solr X.x.x" section. Here are the 4.2.0 Release Notes Also pay attention to any other items in the Detailed Change List that may apply to your instance.
2. Download the latest release and compare the solrconfig.xml and schema.xml in the /example/solr/collection1/conf folder with the same files from the version of Solr from which I am attempting to upgrade (Solr 4.0 in your case). I use a tool like DiffMerge or something similar to help highlight the differences.
3. Examine the differences found in step 2. Research the changes (using Release Notes, Solr Issues Tracker, Solr Wiki, etc.) and determine what impact there will be (if any) with what I have actually implemented in my Solr instance.
4. Stand up a Solr instance running the new version with appropriate config changes for my implementation and then test accordingly.

Yes, I agree that re-indexing is best when you can, as the underlying version of Lucene is changing as well and a re-index will be required to leverage any new features or improvements.

Hope this helps.