Special steps for upgrades from DataStax Enterprise 4.0.0

Due to a bug in DataStax Enterprise 4.0.0, upgrading clusters with search nodes from DataStax Enterprise 4.0.0 to 4.0.x requires special steps to prevent data loss.

This bug impacts upgrades only from DataStax Enterprise 4.0.0.

DataStax is offering a complimentary half-day Upgrade Assessment. This assessment is a DataStax Services engagement designed to assess the upgrade compatibility of your existing DSE deployment to later DSE versions, including 5.1, 6.0, 6.7, and 6.8. Contact the DataStax Services team to schedule your assessment.

Procedure

Drain each node in the cluster, but do not stop the node.

Reload the Solr core.

In the following example, the Solr core is wiki.solr running on the local host on port 8983.

curl -X POST "http://127.0.0.1:8983/solr/admin/cores?action=RELOAD&name=wiki.solr&reindex=false&deleteAll=false"

Upgrade the cluster.
Reindex the Solr core.

In the following example, the Solr core is wiki.solr running on the local host on port 8983.
```
curl -X POST "http://127.0.0.1:8983/solr/admin/cores?action=RELOAD&name=wiki.solr&reindex=true"
```