Not even that. The number of hits returned has a default, which is 10. For more, you choose (the size parameter indicates how many results to return). There is a maximum, by default 100,000 I think.

If you do want to return all results, you can use the scroll API.

There's no guessing with the results in Elasticsearch if you read the (surprisingly accurate) documentation.

Edit (moved from reply to myself): I guess I should clarify before someone corrects me: you could get fewer results than the size parameter. But in that case the total hits should be less than your size parameter and it should be clear that the number of returned documents is the difference.

No, "hits.total" is the total number of documents that matched, regardless of what you specified as the number of hits to return.

Right, but if you set the size to 10, then you either return 10 or (hits.total - 10) documents. If hits.total is greater than 10, you know you returned 10 documents; otherwise, you returned hits.total documents.

Ok, yeah, I see what you're saying and that makes sense. But, even my response is premature because you generally have to parse the whole response to get "hits.total" anyway. So unless you have written a partial parser (does an open source one exist?) you are going to be parsing the whole document to get even "hits.total".

Based on the bug filed[1], "Return number of documents in the result counts as HTTP header or in JSON," the implication is that including the number of documents in the result in the JSON would be an acceptable solution. If that's true, then they're OK with parsing the JSON.

Although, to be fair, the related issue[2] specifically asks for an HTTP header.

JSON parsing is generally pretty fast, but I can understand it being unnecessary overhead (although in general, there are other more significant opportunities for optimization).

If you've ever implemented a JSON stream reader/writer, then you've done partial JSON parsing. Check out the tool `jq`[2], which will parse partial JSON surprisingly well and fast (and this is just a utility).

[1] https://github.com/elastic/elasticsearch/issues/18312

[2] https://github.com/elastic/elasticsearch/issues/16993

[3] https://stedolan.github.io/jq/

The max is 10,000 in 2.x. It was higher before, I forget exactly.

You're right. It can, however, be configured higher using the `index.max_result_window`[1].

[1] https://www.elastic.co/guide/en/elasticsearch/reference/curr...