At the moment, the coordinating node uses the index name from URL and routing values from the query string to forward search requests directly to the shards where they should be executed.

This is very efficient, but does impose some limitations on the choices we can make at execution time. For instance:

• Allow per index routing values in the same query #4272 asks for per-index routing values, which would need to be passed in the body
• Support querying more indices than 4096 bytes-worth #7298 raises the problem of limited space for index names in the URL
• nicer SearchPhaseExecutionException response message for parsing problems #7570 complains about parsing errors being returned from all shards, rather than just one
• Add phase to prefetch doc for query #6719 would allow terms-lookup filters, geo-shape lookup filters, indexed scripts or indexed templates to be fetched just once, instead of by every shard

All of the above (and possibly more?) could be fixed if we parsed the search request in the body. Should we consider doing this? What are the downsides? Would it be worth making it optional?