One of our modules in our project is an elasticsearch cluster.
In order to fine tune the configuration (shards, replicas, mapping, etc.) and the queries, we created a JMeter environment.

I wanted to test a simple query with many different input parameters, which will return results.
I.e. query for documents that exist.

The setup for JMeter is simple.
I created the query I want to check as a POST parameter.
In that query, instead of putting one specific value, which means sending the same values in the query over and over, I used parameter.
I directed JMeter to read from a file (CSV) the parameters.

The next thing was to create that data file.
A file, which consists of rows with real values from the cluster.

For that I used another query, which I ran against the cluster using CURL.
(I am changing some parameters naming)

{
   "fields":[
      "FIELD_1"
   ],
   "size":10000,
   "query":{
      "constant_score":{
         "filter":{
            "bool":{
               "must":[
                  {
                     "term":{
                        "LIVE":true
                     }
                  },
                  {
                     "exists":{
                        "field":"FIELD_1"
                     }
                  }
               ]
            }
         }
      }
   }
}

I piped the result into a file.
Here’s a sample of the file (I changed the names of the index, document type and values for this example):

{
  "took" : 586,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 63807792,
    "max_score" : 1.0,
    "hits" : [ {
      "_index" : "my_index",
      "_type" : "the_document",
      "_id" : "1111111",
      "_score" : 1.0,
      "fields" : {
        "FIELD_1" : "123"
      }
    }, {
      "_index" : "my_index",
      "_type" : "the_document",
      "_id" : "22222222",
      "_score" : 1.0,
      "fields" : {
        "FIELD_1" : "12345"
      }
    }, {
      "_index" : "my_index",
      "_type" : "the_document",
      "_id" : "33333333",
      "_score" : 1.0,
      "fields" : {
        "FIELD_1" : "4456"
      }
    } ]
  }
}

The next thing was parsing this json file, taking only FIELD_1 and put the value in a new file.
For that I used Ruby:

#!/usr/bin/ruby

require 'rubygems'
require 'json'
require 'pp'

input_file = ARGV[0]
output_file = ARGV[1]

json = File.read(input_file)
obj = JSON.parse(json)
hits = obj['hits']

actual_hits = hits['hits']
begin
  file = File.open(output_file, "w")
  actual_hits.each do |hit|
    fields = hit['fields']
    field1 = fields['FIELD_1']
    file.puts(field1)
  end
rescue IOError => e
  # there was an error
ensure
  file.close unless file == nil
end

Important note:
There’s a shorter, better, way to write to file in Ruby:

File.write(output_file, field1)

Unfortunately I can’t use it, as I have older Ruby version and I can’t upgrade it in our sandbox environment.