I'm aware parent child queries are not officially supported, but elasticsearch custom DSL queries are. Upon upgrading from 4.2.1 to 4.3.0 (and still present in 4.4.1) I found that queries that used to work no longer did so.

After quite a bit of tracking down, I found that highlighting was responsible.

Steps to reproduce

curl -XDELETE http://localhost:9200/parent_child
curl -XPUT    http://localhost:9200/parent_child -d '{
  "mappings": {
    "child_type": {
      "properties": {
        "count": {
          "type": "integer"
        }
      },
      "_parent": {
        "type": "parent_type"
      }
    },
    "parent_type": {
      "properties": {
        "name": {
          "type": "string"
        }
      }
    }
  }
}'

curl -XPOST http://localhost:9200/parent_child/_bulk -d'
{ "index": {"_id": 1, "_type": "parent_type" }}
{ "name": "foo" }
{ "index": {"_id": 2, "_parent": 1, "_type": "child_type" }}
{ "count": 2}
{ "index": {"_id": 3, "_parent": 1, "_type": "child_type" }}
{ "count": 2}
'

Issue the query:
{"has_parent":{"query":{"match":{"name":"foo"}},"type":"parent_type"}}

Results in:

Elasticsearch logs showing the error(for reference)

[2016-02-19 15:53:14,966][DEBUG][action.search.type ] [Colonel] [649] Failed to execute fetch phase
RemoteTransportException[[Colonel][127.0.0.1:9300][indices:data/read/search[phase/fetch/id]]]; nested: FetchPhaseExecutionException[Fetch Failed [Failed to highlight field [_routing]]]; nested: IllegalStateException[can't load global ordinals for reader of type: class org.apache.lucene.search.highlight.WeightedSpanTermExtractor$DelegatingLeafReader must be a DirectoryReader];
Caused by: FetchPhaseExecutionException[Fetch Failed [Failed to highlight field [_routing]]]; nested: IllegalStateException[can't load global ordinals for reader of type: class org.apache.lucene.search.highlight.WeightedSpanTermExtractor$DelegatingLeafReader must be a DirectoryReader];
at org.elasticsearch.search.highlight.PlainHighlighter.highlight(PlainHighlighter.java:123)

Upon changing kibana settings to disable highlighting, this same search will return the expected results.

In my opinion highlighting causing any search to not function is unreasonable.

Suggestions for potential solutions include:

• Don't highlight for searches in the Elasticsearch Query DSL
• If a query fails with an error due to highlighting, reissue the search without highlighting
• Anything else you guys can come up with : )