[SOLVED] Does Elasticsearch return partial results when total matches is less than pagination size?

Does Elasticsearch return partial results when total matches is less than pagination size?

I was wondering, considering millions of element. If I have a query with a pagination of 100 elements and there are exactly 100 elements that match my query, does ElasticSearch will always return all of them once, or is there a possibility that it will sometimes return less that 100 elements with a pagination index ?

Solution

The size parameter limits the number of results returned. If the number of matched docs is less than 100, it can return less than 100 results. It can be even 0 results.

Elasticsearch can return "partial results" if there is any issue with shards. By checking the curl API call response you can make sure about it.

{
  "took": 12,
  "timed_out": false,
  "_shards": {
    "total": 5,  <-- number of total shards that hits the query
    "successful": 5,  <-- successfully searched shards.
    "skipped": 0,
    "failed": 0 <-- if you see bigger than 0 the result can be partial
  },
  "hits": {
    "total": {
      "value": 100,  <-- the query hit 100 results.
      "relation": "eq"
    },
    "max_score": 1.5,
    "hits": [ <-- there are 100 objects in the JSON because the size parameter in query is set to 100.
      { "_id": "1", "_source": { "name": "Item 1" } },
      { "_id": "2", "_source": { "name": "Item 2" } },
      ...
      { "_id": "100", "_source": { "name": "Item 100" } }
    ]
  }
}

As a summary answer, if everything works normally If you have a query with a pagination of 100 elements and there are exactly 100 elements that match your query you should always see 100 results in the response body.