Elasticsearch: document size and query performance - elasticsearch

Question

I have an ES index with medium size documents (15-30 Mb more or less).
Each document has a boolean field and most of the times users just want to know if a specific document ID has that field set to true.
Will document size affect the performance of this query?
"size": 1,
"query": {
"term": {
"my_field": True
}
},
"_source": [
"my_field"
]
And will a "size":0 query results in better time performance?

Answer 1

Adding "size":0 to your query, you will avoid some net transfer this behaviour will improve your performance time.
But as I understand your case of use, you can use count
An example query:
curl -XPOST 'http://localhost:9200/test/_count -d '{
"query": {
"bool": {
"must": [
{
"term": {
"id": xxxxx
}
},
{
"term": {
"bool_field": True
}
}
]
}
}
}'
With this query only checking if there is some total, you will know if a doc with some id have set the bool field to true/false depending on the value that you specify in bool_field at query. This will be quite fast.

Answer 2

Considering that Elasticsearch will index your fields, the document size will not be a big problem for the performance. Using size 0 don't affect the query performance inside Elasticsearch but affect positively the performance to retrieve the document because the network transfer.
If you just want to check one boolean field for a specific document you can simply use Get API to obtain the document just retrieving the field you want to check, like this:
curl -XGET 'http://localhost:9200/my_index/my_type/1000?fields=my_field'
In this case Elasticsearch will just retrieve the document with _id = 1000 and the field my_field. So you can check the boolean value.
{
"_index": "my_index",
"_type": "my_type",
"_id": "1000",
"_version": 9,
"found": true,
"fields": {
"my_field": [
true
]
}
}

Answer 3

By looking at your question I see that you haven't mentioned the elasticsearch version you are using. I would say there are lot of factors that affects the performance of a elasticsearch cluster.
However assuming it is the latest elasticsearch and considering that you are after a single value, the best approach is to change your query in to a non-scoring, filtering query. Filters are quite fast in elasticsearch and very easily cached. Making a query non-scoring avoids the scoring phase entirely(calculating relevance, etc...).
To to this:
GET localhost:9200/test_index/test_partition/_search
{
"query" : {
"constant_score" : {
"filter" : {
"term" : {
"my_field" : True
}
}
}
}
}
Note that we are using the search API. The constant_score is used to convert the term query in to a filter, which should be inherently fast.
For more information. Please refer Finding exact values