Problem with _update_by_query

Hi all, i'm using ES v 2.3 and i have a problem with the usage of _update_by_query.
I have some question:
1 - It's a plugin?
2 - I nedd to install it?
3 - I try this POST /test/test/_update_by_query?conflicts=proceed but i have an error:
{
"error": {
"root_cause": [
{
"type": "mapper_parsing_exception",
"reason": "failed to parse, document is empty"
}
],
"type": "mapper_parsing_exception",
"reason": "failed to parse, document is empty"
},
"status": 400
}
i see the log...and ES try to create a new document:
[rest.suppressed ] /test/test/_update_by_query Params: {conflicts=proceed, index=test, id=_update_by_query, type=test}
....It's a bug? or i wrong something?

Someone can help me????

It is a module. Modules are plugins that come pre-bundled. It makes my life easier to develop it this way but it has caused some trouble folks using the transport client, trouble we're trying to fix in 5.0.

No, it comes pre-installed.

It looks like it isn't installed. Weird.

When you started Elasticsearch you should have a log line that looks like

[2016-07-21 12:06:22,221][INFO ][plugins                  ] [Gauntlet] modules [reindex, lang-expression, lang-groovy], plugins [], sites []

That is what I get from a fresh download of 2.3.3 I had laying around on my laptop. Is reindex in the list?

Can you post the output of find modules run from the root of you Elasticsearch install? That should include something that looks like:

modules/reindex
modules/reindex/plugin-descriptor.properties
modules/reindex/reindex-2.3.3.jar

You also might want to check curl localhost:9200/_nodes/_all/plugins?pretty. That should list the plugins the same as that logger line on startup.