CODEWITHSUNDEEP
elasticsearch
Kong
Kong

Reputation: 9546

Does Elasticsearch have a Default Sort Order for Filter Queries?

Does Elasticsearch have a defined default sort order for filter queries if none is specified? Or is it more like an RDBMS without an order by - i.e. nothing is guaranteed?

From my experiments I appear to be getting my documents back in order of their id - which is exactly what I want - I am just wondering if this can be relied on?

Upvotes: 0

Views: 1744

Answers (2)

pmishev
pmishev

Reputation: 976

No, the order cannot be relied on (in ES 7.12.1 at least)!

I've tested in a production environment, where we have a cluster with multiple shards and replicas and even running the simplest query like this returns results in different order on every few requests:

POST /my_index/_search

One way to ensure the same order is to add order by _id, which seems to bring a small performance hit with it.

Also, I know it's not related to this question, but keep in mind that if you do have scoring in your query and you still get random results, even after adding an order by _id, the problem is that the scores are randomly generated in a cluster environment. This problem can be solved with adding a parameter to you query:

POST /my_index/_search?search_type=dfs_query_then_fetch

More info and possible solutions can be found here: https://www.elastic.co/guide/en/elasticsearch/reference/7.17/consistent-scoring.html

Upvotes: 0

Val
Val

Reputation: 217274

When you only have filters (i.e. no scoring) and no explicit sort clause, then the documents are returned in index order, i.e. implicitly sorted by the special field named _doc.

Index order simply means the sequential order in which the documents have been indexed.

If your id is sequential and you've indexed your documents in the same order as your id, then what you observe is correct, but it might not always be the case.

Upvotes: 2

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