It would be a great addition if an already existing index could be refreshed:

• Katta would examine the HDFS index directory to see, which shards are there
• Depending on the shard directory name it could deduct if the shard is already present on the nodes and doesn't need to be copied or
• If there are new shards that are not already distributed. It would automatically start copy them over to the shards.
• After the deployment is done it switches all search traffic to the refreshed index automatically.

Assumptions:

• It is okay for refreshed indexes to have deleted events not automatically removed (or the client needs to filter those out through an add'l deleted field)
• Shard names are unique and incremental updates into the shard directory will have a unique name to avoid collisions.

This would be a great enhancement considering that it would cut down deployment time for large indexes dramatically and simplify the overall client code (the current API makes it necessary to have multiple rolling indexes to incorporate updates).