Random order & pagination Elasticsearch

Question

In this issue is a feature request for ordering with optional seed allowing for recreation of random order.

I need to be able to paginate random ordered results. How could this be be done with Elasticsearch 0.19.1 ?

Thanks.

Answer 1

This should be considerably faster than both answers above and supports seeding:

curl -XGET 'localhost:9200/_search' -d '{   "query": {     "function_score" : {       "query" : { "match_all": {} },       "random_score" : {}     }   } }'; 

See: https://github.com/elasticsearch/elasticsearch/issues/1170

Answer 2

You can sort using a hash function of a unique field (for example id) and a random salt. Depending on how truly random the results should be, you can do something as primitive as:

{   "query" : { "query_string" : {"query" : "*:*"} },   "sort" : {     "_script" : {          "script" : "(doc['_id'].value + salt).hashCode()",         "type" : "number",         "params" : {             "salt" : "some_random_string"         },         "order" : "asc"     }   } } 

or something as sophisticated as

{   "query" : { "query_string" : {"query" : "*:*"} },   "sort" : {     "_script" : {          "script" : "org.elasticsearch.common.Digest.md5Hex(doc['_id'].value + salt)",         "type" : "string",         "params" : {             "salt" : "some_random_string"         },         "order" : "asc"     }   } } 

The second example will produce more random results but will be somewhat slower.

For this approach to work the field _id has to be stored. Otherwise, the query will fail with NullPointerException.