Trying to set the max_gram and min_gram in Elasticsearch

I have faced a similar issue and below error message is clearly explaining the issue.

[400] {"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"The difference between max_gram and min_gram in NGram Tokenizer must be less than or equal to: 1 but was [49]. This limit can be set by changing the [index.max_ngram_diff] index level setting."}],"type":"illegal_argument_exception","reason":"The difference between max_gram and min_gram in NGram Tokenizer must be less than or equal to: 1 but was [49]. This limit can be set by changing the [index.max_ngram_diff] index level setting."},"status":400}

Basically, by Default, the difference between max_gram and min_gram in NGram Tokenizer can't be more than 1 and if you want you to change this, then in your index settings you need to change it by adding below setting.

"max_ngram_diff" : "50" --> you can mention this number accoding to your requirement.

Below is my index settings, where you can see I have a difference of 47 in my max_gram and min_gram hence set max_ngram_diff to 50.

{     "settings": {        "index": {            "analysis": {                "analyzer": {                    "prefix": {                        "type": "custom",                        "filter": [                            "lowercaseFilter"                        ],                        "tokenizer": "edgeNGramTokenizer"                    }                },                "tokenizer": {                    "edgeNGramTokenizer": {                        "token_chars": [                            "letter",                            "digit"                        ],                        "min_gram": "1",                        "type": "edgeNGram",                        "max_gram": "40"                    },                    "loginNGram": {                        "type": "nGram",                        "min_gram": "3",                        "max_gram": "50"                    }                }            },            "number_of_shards": "1",            "number_of_replicas": "0",            "max_ngram_diff" : "50"        }    }} 

Edit: Adding an official Elastic documentation, which explains that default length of max_gram is 2 and min_gram is 1, hence default difference between these can't be more than 1, hence the exception. And then snippet from the same doc

The index level setting index.max_ngram_diff controls the maximum allowed difference between max_gram and min_gram.

One can also use an index template to apply the setting automatically to all new indices:

curl -X PUT "localhost:9200/_index_template/template_1?pretty" -H 'Content-Type: application/json' -d'{  "index_patterns": [      "*"  ],  "template": {    "settings": {      "index": {         "max_ngram_diff": 50      }    }  }}'

The template will not be deleted by removing every index, but has to be removed manually:

curl -X DELETE "localhost:9200/_index_template/template_1