Allow to use the "update" action in update challenges about rally-tracks

[jmeagher]

Adding a specific use case we use ElasticSearch for the searching capability instead of trying that with our database layer. The indexing workload ends up being about 90% updates and 10% indexes. All operations are done via the /_bulk endpoint.

A typical index vs update flow would look like:

• Index to create the initial document with 50-100 fields
• Update 3-4 fields or nested documents on a daily to weekly basis

[danielmitterdorfer]

Thanks for the use case. To me this sounds as if this should be solved with a dedicated corpus that includes documents and the corresponding action-and-meta-data line though because the documents that should be updated need to be crafted specifically. The approach we use here instead is to simulate id conflicts randomly (but based on a configurable probability) and then emit either an index or update action in the corresponding meta-data line but we always use the full document. Hope that makes sense now with my additional explanation.