Elastic Search : Meta-Data/Indices

ES provides near real time search capabilities.

Shards: Number of pieces the data is going to be divided.

Replicas: This is a failover mechanism ES provides in case the primary goes off line or fails.

Data Type:Text Vs Keyword
Text: Use  type as 'Text' when it requires full-text and relevancy search in documents.


Keyword: This is required when searching is based on exact value.Many operation like filtering, sorting, aggregation requires exact value.

Alisases:

• Switch transparently between one index and another on a running cluster

• Group multiple indices (for example, last_three_months)

• Create “views” on a subset of the documents in an index

Aliases gives the following:

Add/ Remove indices to aliases

POST /_aliases

{

    "actions" : [

        { "remove" : { "index" : "test1", "alias" : "employee" } },

        { "add" : { "index" : "test2", "alias" : "employee" } }

    ]

}

POST /_aliases
{
    "actions" : [
        { "add" : { "indices" : ["employee-primary", "employee-secondary"], "alias" : "employee" } }
    ]
}

Associating main and backup/old indexes/indices for a given context employee:

GET /sample-app-index-spec/metadata/employee

Create Index to metadata

PUT /sample-app-index-spec/emp-metadata/employee

{

"context":"employee",

"main" : "employee-version2",

"previous": "employee-version1"

}

Get mapping :

GET employee/_mapping

GET employee-primary/_mapping

Get all aliases: GET _aliases,  get _cat/aliases

Get all indices: GET _cat/indices
Dilete all indice: DELETE INDEX_NAME

Adding a new node element:
"mappings": {
  "employee": {
    "preferredLocations": {
      "properties": {
        "city": {
          "properties": {
            "value": {
              "type": "text",
              "fields": {
                "keyword": {
                  "type": "keyword",
                  "ignore_above": 256
                }
              }
            }
          }
        }
      },
      "currenltLocations": {
       
      }
    }

Note: depending upon properties type text/keyword/number query performance will vary.

#. To make element searchable it should available in the mapping document. so that it is getting indexed and query can be made as per the mapping. If the element is not going to be searchable the new element can be added without part of mapping