Elasticsearch - Notes

• GET vs. POST
• index
• type
• document
  • settings
  • mapping

GET vs. POST

1. https://www.elastic.co/guide/en/elasticsearch/guide/current/_empty_search.html

https://stackoverflow.com/questions/978061/983458#comment53906725_983458

Elasticsearch is a fairly major product that utilises HTTP request bodies in GET. According to their manual whether a HTTP request should support having a body or not is undefined. I’m personally not comfortable with populating a GET request body, but they seem to have a different opinion and they must know what they’re doing.

https://stackoverflow.com/a/36940185

Although the RFC does not mention that you can’t have a body with GET. So Elasticsearch supports also POST.

• it’s possible to use both GET and POST requests for queries which must be GET requests semantically (say, search requests)
• it’s possible to pass all parameters in JSON request body in both GET and POST requests

index

1. https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-create-index.html

it’s not necessary to create index separately - it’s created automatically when the first document is added to this index.

type

https://www.elastic.co/guide/en/elasticsearch/reference/6.x/removal-of-types.html#_schedule_for_removal_of_mapping_types

Indices created in 6.x only allow a single-type per index. Any name can be used for the type, but there can be only one. The preferred type name is _doc, so that index APIs have the same path as they will have in 7.0: PUT {index}/_doc/{id} and POST {index}/_doc.

document

https://www.elastic.co/guide/en/elasticsearch/guide/2.x/document.html

In Elasticsearch, the term document has a specific meaning. It refers to the top-level, or root object that is serialized into JSON and stored in Elasticsearch under a unique ID.

settings

https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-create-index.html

You do not have to explicitly specify index section inside the settings section.

{
  "settings" : {
    "number_of_shards" : 3,
    "number_of_replicas" : 2
  }
}

is equivalent to:

{
  "settings" : {
    "index" : {
      "number_of_shards" : 3,
      "number_of_replicas" : 2
    }
  }
}

mapping

1. https://www.elastic.co/blog/found-elasticsearch-mapping-introduction

If you do not specify a mapping, Elasticsearch will by default generate one dynamically when detecting new fields in documents during indexing. However, this dynamic mapping generation comes with a few caveats.

1. Detected types might not be correct.
2. May lead to unnecessary duplication. (The _source field and _all field especially)
3. Uses default analyzers and settings for indexing and searching.

=> specify mapping explicitly.