Does _delete_by_query need a plugin or not? ES version 5.5

[makons]

So I've seen this post from way before in 2015 saying that delete by query is supported through a plugin delete-by-query. This was for the Elasticsearch version 2.0.0. However, there's a newer post which says that now this function is inside the core API, and no plugin is needed. If I got it correctly, newer update is valid from version 5.0 onwards.

Now, my problem is that Elasticsearch does not recognise _delete_by_query function, and inserts a document with that function name as its ID - _id: "_delete_by_query". This happens if I run:

POST <index_name>/<mapping_name>/_delete_by_query
{
    "query": { ... }
}

If I try to call it without the specified mapping:

POST <index_name>/_delete_by_query
{
    "query": { ... }
}

I get an error:

{
    "type": "invalid_type_name_exception",
    "reason": "Document mapping type name can't start with '_', found: [_delete_by_query]"
}

This post mentions that the error happens if the plugin is needed, and ES cannot recognise the _delete_by_query function. I'm running Elasticsearch 5.5.2, so how could that be possible? If this is not the case, what causes then this behaviour?

[warkolm (Mark Walkom)]

FYi 5.X has been EOL for quite some time, you should really upgrade as a matter of urgency.

The docs show this as an example, with no type defined;

POST twitter/_delete_by_query
{
  "query": { 
    "match": {
      "message": "some message"
    }
  }
}

If that's not working, what does your query look like?

[makons]

Thanks for the reply, as well as version change suggestion, I'll look into that!

So, my query is like this:

POST <index_name>/_delete_by_query?routing=<parent_type>
{
  "query" : {
    "bool" : {
      "must_not" : [
        {
          "has_parent" : {
            "query" : {
              "match_all" : {
                "boost" : 1.0
              }
            },
            "parent_type" : <parent_type>,
            "score" : false,
            "ignore_unmapped" : false,
            "boost" : 1.0
          }
        }
      ],
      "disable_coord" : false,
      "adjust_pure_negative" : true,
      "boost" : 1.0
    }
  }
}

I've tried both that and POST <index_name>/<child_type>/_delete_by_query?routing=<parent_type> with the same query. When child type is specified, the record is inserted in the ES with _id="_delete_by_query", but when I leave it out I get that invalid_type_name_exception.

However, I did decent amount of digging and found this topic that seems to be related to my issue. I indeed run an embedded instance for testing purposes, and _delete_by_query is not supported there. The workaround mentioned was to include reindex plugin in the elasticsearch configuration. I haven't been able to make that workaround work, but in the end, as the last comment on that thread says, it's not a reliable solution.

In the end, I'll most likely drop this unit test that I had trouble with, and only rely on the integration test that uses a standalone elasticsearch server, which does support _delete_by_query.