ElasticSearch Notes

ElasticSearch Notes

```
Index is like a database
Index can be splited into shared shared accross multiple nodes (it can have replicas)
A node can have more than 1 shards
Each shards is an instance of lucene - and they hence scales horizontally
Schema of the documents are defined by -- "the Type"

Inverted indices - quickly maps the search

Calcualations of shards in a cluster:
Index configured with 5 primary & 3 replicas ==> 20 shards
```
Mapping -- the schema definition (sometimes you need to customize)




##Using Curl to add a single document to the ES
curl -H "Content-Type: application/json" -XPUT 127.0.0.1:9200/movies/movie/109487 -d '
{ "genre" : ["IMAX","Sci-Fi"],
"title" : "Interstellar",
"year" : 2014
}'

## get data from an index: movies of "Type" movie
curl -H "Content-Type: application/json" -XGET 127.0.0.1:9200/movies/movie/_search?pretty

#bulk upload
  157  curl -H "Content-Type: application/json" -XPUT 127.0.0.1:9200/_bulk?pretty --data-binary @movies.json
# retrieve all movies
  158  curl -H "Content-Type: application/json" -XGET 127.0.0.1:9200/movies/_search?pretty


##################### Some commands 

First the document was created by using the http 'PUT':

curl -H "Content-Type: application/json" -XPUT 127.0.0.1:9200/movies/movie/109487 -d '{ "genre" : ["IMAX","Sci-Fi"],"title" : "Interstellar","year" : 2014}'

Then the bulk import failed as the document already exist with this :

curl -H "Content-Type: application/json" -XPUT 127.0.0.1:9200/_bulk?pretty --data-binary @movies.json  

Then used the http 'POST' to update the document using this:

curl -H "Content-Type: application/json" -XPOST 127.0.0.1:9200/movies/movie/109487/_update -d '{ 

"doc" : {

       "title": "Interstellar Woo"    

}

}'

Inserting again:

curl -H "Content-Type: application/json" -XPUT 127.0.0.1:9200/movies/movie/109487?pretty -d '

{ "genre" : ["IMAX","Sci-Fi"],"title" : "Interstellar","year" : 2014}'

########################################################

curl -H "Content-Type: application/json" -XDELETE 127.0.0.1:9200/movies/_search?q=Dark   << This a search

#Delete a document
curl -H "Content-Type: application/json" -XDELETE 127.0.0.1:9200/movies/movie/123?pretty


###Handling Concurrency:
Uses version for documents 
retry_on_conflicts=N "to automatically retry"


### Using Analyzers
Keywords -- will do exact matching when searching (so no analyzing)
text -- will allow analyzing or partial matching 


##Search
curl -H "Content-Type: application/json" -XGET 127.0.0.1:9200/movies/movie/_search?pretty -d '
{ "query" : { "match" : { "title" : "Star Trek" }}}'

The above search return multiple movies as title is not set as a keyword
{
  "took" : 36,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 2,
    "max_score" : 0.77904123,
    "hits" : [
      {
        "_index" : "movies",
        "_type" : "movie",
        "_id" : "122886",
        "_score" : 0.77904123,
        "_source" : {
          "id" : "122886",
          "title" : "Star Wars: Episode VII - The Force Awakens",
          "year" : 2015,
          "genre" : [
            "Action",
            "Adventure",
            "Fantasy",
            "Sci-Fi",
            "IMAX"
          ]
        }
      },
      {
        "_index" : "movies",
        "_type" : "movie",
        "_id" : "135569",
        "_score" : 0.5753642,
        "_source" : {
          "id" : "135569",
          "title" : "Star Trek Beyond",
          "year" : 2016,
          "genre" : [
            "Action",
            "Adventure",
            "Sci-Fi"
          ]
        }
      }
    ]
  }
}


#### Cannot remap an index. For this the index will need to be deleted and will recreated

#delete an index
curl -H "Content-Type: application/json" -XDELETE 127.0.0.1:9200/movies

#now searching in the deleted index gives 404 error

curl -H "Content-Type: application/json" -XGET 127.0.0.1:9200/movies/movie/_search?pretty -d '
{ "query" : { "match" : { "title" : "Star Trek" }}}'
{
  "error" : {
    "root_cause" : [
      {
        "type" : "index_not_found_exception",
        "reason" : "no such index",
        "resource.type" : "index_or_alias",
        "resource.id" : "movies",
        "index_uuid" : "_na_",
        "index" : "movies"
      }
    ],
    "type" : "index_not_found_exception",
    "reason" : "no such index",
    "resource.type" : "index_or_alias",
    "resource.id" : "movies",
    "index_uuid" : "_na_",
    "index" : "movies"
  },
  "status" : 404
}