Original comment by @dimitris-athanasiou:

This issue is to track work necessary for supporting rolling the state index. We can add tasks as we identify them.

• Add read/write aliases
• For quantiles, check for existing and write to the same index any old quantiles are in
• For data frame analytics progress, check for existing and write to the same index any old progress documents are in
• For persistent state document, check for existing and write to the same index any old documents are in
• Make sure that all get requests for state documents are replaced with ID query _search requests that ignore duplicates
• Make sure all deletes can handle multiple indices
• Make sure index template has a wildcard so new state indices get the template
• Use ILM or other mechanism to create new state indices when the current one reaches a certain size
• Remove empty state indices during nightly maintenance