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Elasticsearch Knowledges ​

Index in Elasticsearch ​

  • Index: A set of same types of document.
  • Mapping: Field constraint information for documents in an index, similar to structural constraints for tables.

Forward Index and Inverted Index ​

The elasticsearch adopt Inverted Index:

  • document: each data is a document.
  • term: grouping of words in a document based on semantics.

Forward Index ​

Based on document id to create index. When search terms, it must find the document at first, then check the document if includes terms.

idtitleprice
1apple watch1999
2apple care523
3huawei headphone600
4apple mac4500

Inverted Index ​

Segment the document content and create an index of the terms and record the information (id) of the document where the terms are located. In the query first according to the term query to the document id, and then get the corresponding document.

termdocument id
apple1, 2, 3, 6
watch2,
care3,
huawei4, 5
headphone5
mac6

MySql vs Elasticsearch compare ​

MySQLElasticsearchDescription
TableIndexIndex is a set of document, similar to the table in database.
RowDocumentDocument is each data, similar to the rows in database. All documents are JSON format.
ColumnFieldField is fields in a json document, similar the Column in database.
SchemaMappingMapping is the constraints of document in Index, such as field type constraints. It is similar to Schema in database.
SQLDSLDSL is a JSON-style request statement provided by elasticsearch to manipulate elasticsearch and implement CRUD.
  • Architecture
    • MySQL: it specialises in transaction type operations that ensure data security and consistency.
    • Elasticsearch: it is good at searching, analysing, and calculating large amounts of data.

Elasticsearch

Index Library Operator ​

Mapping feild ​

mapping is a constraint on documents in an indexed library, common mapping attributes include:

  • type: field data type
    • string: text (text that can be segmented), keyword (e.g., brand, Country, ip address)
    • number: long, integer, short, byte, double, float
    • bool: boolean
    • date: date
    • object: object
  • index: whether to create an index, default value: true
  • analyzer: use which analyzer
  • properties: the sub-field of current field

Create Index Library ​

In ES to operate the index library and document via RESTful request. Using DSL syntax to represent request content. The dsl syntax for creating index libraries and mapping is as follows:

dsl
PUT /index_library_name
{
  "mappings":{
    "properties":{
      "field name":{
        "type": "keyword",
        "analyzer": "ik_smart"
      },
      "field name2":{
        "type": "keyword",
        "index": false
      },
      "field name3":{
        "properties":{
          "sub field"{
            "type": "keyword"
          }
        }
      }
    }
  }
}
PUT /index_library_name
{
  "mappings":{
    "properties":{
      "field name":{
        "type": "keyword",
        "analyzer": "ik_smart"
      },
      "field name2":{
        "type": "keyword",
        "index": false
      },
      "field name3":{
        "properties":{
          "sub field"{
            "type": "keyword"
          }
        }
      }
    }
  }
}
  • example
dsl
PUT /test
{
  "mappings":{
    "properties":{
      "info":{
        "type": "text",
        "analyzer": "ik_smart"
      },
      "email":{
        "type": "keyword",
        "index": "false"
      },
      "name":{
        "type": "object",
        "properties":{
          "firstName":{
            "type":"keyword"
          },
          "lastName":{
            "type":"keyword"
          },
        }
      }
    }
  }
}
PUT /test
{
  "mappings":{
    "properties":{
      "info":{
        "type": "text",
        "analyzer": "ik_smart"
      },
      "email":{
        "type": "keyword",
        "index": "false"
      },
      "name":{
        "type": "object",
        "properties":{
          "firstName":{
            "type":"keyword"
          },
          "lastName":{
            "type":"keyword"
          },
        }
      }
    }
  }
}

Check Index Library ​

  • syntax for cheching index library
dsl
GET /Index_Library_name
GET /Index_Library_name
  • Example
dsl
GET /test
GET /test

Delete Index Library ​

  • Syntax for deleting index library
dsl
DELETE /Index_Library_name
DELETE /Index_Library_name
  • Example
dsl
DELETE /test
DELETE /test

Update Index Library ​

By default, elasticsearch is forbidden to modify the index database, when the index lirary and mapping created. However, we can add new fields into index library:

dsl
PUT /Index_Library_name/_mapping
{
  "properties":{
    "new field name":{
      "type":"integer"
    }
  }
}
PUT /Index_Library_name/_mapping
{
  "properties":{
    "new field name":{
      "type":"integer"
    }
  }
}
  • Example
dsl
PUT /test/_mapping
{
  "properties":{
    "age":{
      "type":"integer"
    }
  }
}
PUT /test/_mapping
{
  "properties":{
    "age":{
      "type":"integer"
    }
  }
}
  • Note: the new field name cannot same as before.

Document Operator ​

Add new documents ​

  • Syntax
dsl
POST /Index_library/_doc/document_id
{
  "field 1": "value 1",
  "field 2": "value 2",
  "field 3": {
    "sub-field 1": "value 3",
    "sub-field 2": "value 4"
  }
}
POST /Index_library/_doc/document_id
{
  "field 1": "value 1",
  "field 2": "value 2",
  "field 3": {
    "sub-field 1": "value 3",
    "sub-field 2": "value 4"
  }
}
  • Example
dsl
POST /test/_doc/1
{
  "info": "This is my first document",
  "email": "jiuxiaohong@gmail.com",
  "name": {
    "firstName": "Xiaohong",
    "lastName": "Jiu"
  }
}
POST /test/_doc/1
{
  "info": "This is my first document",
  "email": "jiuxiaohong@gmail.com",
  "name": {
    "firstName": "Xiaohong",
    "lastName": "Jiu"
  }
}

Check document ​

  • Syntax
dsl
GET /Index_library_Name/_doc/document_id
GET /Index_library_Name/_doc/document_id
  • Example
dsl
GET /test/_doc/1
GET /test/_doc/1

Delete document ​

  • Syntax
dsl
DELETE /Index_library_Name/_doc/document_id
DELETE /Index_library_Name/_doc/document_id
  • Example
dsl
DELETE /test/_doc/1
DELETE /test/_doc/1

Update document ​

Full-scale modification (global modification) ​

It will delete the old document, then insert new ducoment.

  • Syntax
dsl
PUT /Index_library_Name/_doc/document_id
{
  "field 1": "value 1",
  "field 2": "value 2",
}
PUT /Index_library_Name/_doc/document_id
{
  "field 1": "value 1",
  "field 2": "value 2",
}
  • Example
dsl
PUT /test/_doc/1
{
  "info": "This is my first document",
  "email": "matiao@gmail.com",
  "name": {
    "firstName": "Tiao",
    "lastName": "Ma"
  }
}
PUT /test/_doc/1
{
  "info": "This is my first document",
  "email": "matiao@gmail.com",
  "name": {
    "firstName": "Tiao",
    "lastName": "Ma"
  }
}

Incremental change (local modification) ​

It need user specify the field.

  • Syntax
dsl
POST /Index_library_Name/_update/document_id
{
  'doc':{
    "field 1": "new value"
  }
}
POST /Index_library_Name/_update/document_id
{
  'doc':{
    "field 1": "new value"
  }
}
  • Example
dsl
POST /test/_update/1
{
  'doc':{
    "email": "matiao@gmail.com"
  }
}
POST /test/_update/1
{
  'doc':{
    "email": "matiao@gmail.com"
  }
}

RestClient ​

RestClient operate Index library ​

It is a client provided by elasticsearc used to operate ES. The essence of these clients is to assemble DLS statements and send them to ES via http requests.

  • Create index library
  • Delete inde library
  • Checking for the existence of indexed libraries