elasticsearch: how to free store size after deleting documents

Deleting documents only flags these as deleted, so they would not be searched. To reclaim disk space, you have to optimize the index:

curl -XPOST 'http://localhost:9200/_optimize?only_expunge_deletes=true'

documentation: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/indices-optimize.html

The documentation has moved to: https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-forcemerge.html

Update

Starting with Elasticsearch 2.1.x, optimize is deprecated in favor of forcemerge. The API is the same, only the endpoint did change.

curl -XPOST 'http://localhost:9200/_forcemerge?only_expunge_deletes=true'

In the current elasticsearch version(7.5),

1. To optimize all indices:

   POST /_forcemerge?only_expunge_deletes=true

2. To optimize single index

   POST /twitter/_forcemerge?only_expunge_deletes=true , where twitter is the index

3. To optimize several indices

   POST /twitter,facebook/_forcemerge?only_expunge_deletes=true , where twitter and facebook are the indices

Reference: https://www.elastic.co/guide/en/elasticsearch/reference/7.5/indices-forcemerge.html#indices-forcemerge

knutwalker's answer is correct. However if you are using AWS ElasticSearch and want to free storage space, this will not quite work.

On AWS the index to forgemerge must be specified in the URL. It can include wildcards as is common with index rotation.

curl -XPOST 'https://something.es.amazonaws.com/index-*/_forcemerge?only_expunge_deletes=true'

AWS publishes a list of ElasticSearch API differences.