The update handler needs an overhaul.
A few goals I think we might want to look at:
1. Cleanup - drop DirectUpdateHandler(2) line - move to something like UpdateHandler, DefaultUpdateHandler
2. Expose the SolrIndexWriter in the api or add the proper abstractions to get done what we now do with special casing:
3. Stop closing the IndexWriter and start using commit (still lazy IW init though).
4. Drop iwAccess, iwCommit locks and sync mostly at the Lucene level.
5. Keep NRT support in mind.
6. Keep microsharding in mind (maintain logical index as multiple physical indexes)
7. Address the current issues we face because multiple original/'reloaded' cores can have a different IndexWriter on the same index.