Compare IDs between two indices in elasticsearch

Question

I have two indices in an elasticsearch cluster, containing what ought to be the same data in two slightly different formats. However, the number of records are different. The IDs of each document should be the same. Is there a way to extract a list of what IDs are present in one index but not the other?

Answer 1

If your two indices have the same type where these documents are stored, you can use something like this:

GET index1,index2/_search
{
  "size": 0,
  "aggs": {
    "group_by_uid": {
      "terms": {
        "field": "_uid"
      },
      "aggs": {
        "count_indices": {
          "cardinality": {
            "field": "_index"
          }
        },
        "values_bucket_filter_by_index_count": {
          "bucket_selector": {
            "buckets_path": {
              "count": "count_indices"
            },
            "script": "params.count < 2"
          }
        }
      }
    }
  }
}

The query above works in 5.x. If your ID is a field inside a document, that's even better to test.