What does total value shows inside the _search query result in elasticsearch? - elasticsearch

Question

When we call the elasticsearch, say as follows:
POST https:////_search with body:
{
"from": 0,
"size": 1,
"query": {
"bool": {
"must": [
{
"range": {
"createdAt": {
"gt": "2019-11-11T10:00:00"
}
}
}
]
}
},
"sort": [
{
"createdAt" : {
"order" : "desc"
}
}
]
}
I see that I get only 1 result as pagination is set to 1 but total inside hits in response shows 2. This is the response I get:
{
"took": 4,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": {
"value": 2,
"relation": "eq"
},
"max_score": null,
"hits": [
{
"_index": “<index-name>”,
"_type": "_doc",
"_id": "5113c843-dff3-499f-a12e-44c7ac103bcf_0",
"_score": null,
"_source": {
"oId": "5113c843-dff3-499f-a12e-44c7ac103bcf",
"oItemId": 0,
"createdAt": "2019-11-13T11:00:00"
},
"sort": [
1573642800000
]
}
]
}
}
Doesn’t total doesn’t capture the pagination part? And it only cares about the query report? It should show the total count of items matching the query irrespective of the pagination set, right?

Answer 1

Yes, You are right that total doesn't capture the pagination part and just cares about the query report ie. whatever the total no of the document matches for a given query.
To be precise, it is as explained in official ES docs .
total (Object) Metadata about the number of returned documents.
Returned parameters include:
value: Total number of returned documents. relation: Indicates whether
the number of documents returned. Returned values are:
eq: Accurate gte: Lower bound, including returned documents
It means its the total no of returned documents, but as pagination is set to 1 in your example, inner hits have just 1 document.You can cross-check this understanding easily by creating a sample example as below:
Create a sample index with just 1 text field:
URL:- http://localhost:9200/{your-index-name}/ --> PUT method
{
"mappings": {
"properties": {
"name": {
"type": "text"
}
}
},
"settings": {
"index": {
"number_of_shards": "1",
"number_of_replicas": "1"
}
}
}
Once the above index is created index below 4 documents:
URL:- http://localhost:9200/{your-index-name}/_doc/{1,2,like..} --> POST method
{
"name": "foo 1"
}
{
"name": "foo bar"
}
{
"name": "foo"
}
{
"name": "foo 2"
}
Now when you hit below search query without pagination:
{
"query": {
"bool": {
"must": [
{
"match": {
"name": "foo"
}
}
]
}
}
}
It gives below response:
{
"took": 9,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"skipped": 0,
"failed": 0
},
"hits": {
"total": {
"value": 4, --> Note 4 here
"relation": "eq"
},
"max_score": 0.12199639,
"hits": [
{
"_index": "59638303",
"_type": "_doc",
"_id": "1",
"_score": 0.12199639,
"_source": {
"name": "foo"
}
},
{
"_index": "59638303",
"_type": "_doc",
"_id": "3",
"_score": 0.12199639,
"_source": {
"name": "foo"
}
},
{
"_index": "59638303",
"_type": "_doc",
"_id": "2",
"_score": 0.09271725,
"_source": {
"name": "foo bar"
}
},
{
"_index": "59638303",
"_type": "_doc",
"_id": "4",
"_score": 0.09271725,
"_source": {
"name": "foo 1"
}
}
]
}
}
But when you hit a search query with pagination:
{
"from": 0,
"size": 1,--> note size 1
"query": {
"bool": {
"must": [
{
"match": {
"name": "foo"
}
}
]
}
}
}
it gives below response
{
"took": 23,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"skipped": 0,
"failed": 0
},
"hits": {
"total": {
"value": 4, --> this is still 4
"relation": "eq"
},
"max_score": 0.12199639,
"hits": [
{
"_index": "59638303",
"_type": "_doc",
"_id": "1",
"_score": 0.12199639,
"_source": {
"name": "foo"
}
}
]
}
}
Now in the above query, you can change the size and check only inner-hits array gets change but the outer hits object which contains total always remains same as 4, this confirms your understanding is correct.