How to turn off caching when testing Elastic Search

Before I answer, a disclaimer that I agree with the comments on the question, disabling cache is not the best way to stress test Elasticsearch. Hitting it with simultaneous queries that are representative of your production query set along with active indexing at the same time is going to be a far better way to see how ES responds under load.

However, to answer your question and point out some caveats:

1. You can clear your cache in between runs:

   The clear cache API allows to clear either all caches or specific cached associated with one ore more indices.

   https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-clearcache.html

2. You can turn off your filter cache by setting index.cache.filter.type to none - this will prevent filter results from being cached:

   http://elasticsearch-users.115913.n3.nabble.com/Disable-cache-td3825105.html

   http://elasticsearch-users.115913.n3.nabble.com/Disabling-cache-td3201850.html

3. You can change the settings for the field data cache - however I don't know what will happen if you set this to zero:

   https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-fielddata.html

4. Overall, though, keep in mind that Elasticsearch makes significant use of the native OS filesystem cache, so much of "caching" is happening outside the control of ES:

   https://blog.codecentric.de/en/2014/05/elasticsearch-indexing-performance-cheatsheet/

GET /my_index/_search?request_cache=false

https://www.elastic.co/guide/en/elasticsearch/reference/current/shard-request-cache.html