Support for percolating via an alias is already implemented via #3173, if an alias is resolved to more than one index, then from the response it is impossible to know what id belongs to what concrete index. This can become even a bigger issue if percolate queries with the same id exist in different indices.

For this reason the response needs to be enhanced to include the concrete index per match:

{
  "matches" : [
      {
         "id" : "1",
         "_index" : "my-index1"
      },
      ...
  ]
}

The current format will still be supported by setting percolate_format=ids parameter in the query string. Useful in the case percolation is only executed on just one index.

This issue will also add support for specifying multiple indices in the percolate request:

curl -XGET 'localhost:9200/my-index1,my-index2/my-type/_percolate' -d '...'