Looping over all documents in an elasticsearch index

Question

Using the Elasticsearch javascript client (node.js), what is the best (or simplest) way to loop through every document in an index (ca. 100 000 documents)?

Answer 1

I think a good place to start is with scan queries using the scroll api:

https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-scroll.html

Basically it's similar to a cursor with a database - you open the query with a time limit and it returns a scroll id. You then use that scroll id to retrieve the first batch of results and it returns the documents along with a new scroll id. Examples below:

curl -XGET 'localhost:9200/_search?search_type=scan&scroll=10m&size=1000' -d '
{
    "query" : {
        "match_all" : {}
    }
}
'

This will return a _scroll_id that you then use to retrieve documents:

curl -XGET 'localhost:9200/_search/scroll?scroll=10m' -d '<_SCROLL_ID_HERE>'

Note that this will return 1000 documents PER PRIMARY SHARD - so if you have 4 primary shards it will return 4000 documents. Each call will in addition to the documents return a new _scroll_id which you then use for the next call. The "scroll=10m" sets a time limit of 10m to keep the scroll open between calls.