Question about prequery of DFS_Query_then_Fetch

Elastic Stack Elasticsearch
1

Hello,
I have a simple question about "prequery" step of "DFS_Query_then_Fetch" search type.
When we create an index of only 1 primary shard and make 4 replicas,
is "prequery" excuted for all 5 shards(primary and replicas) in this case?

Thanks for your help always!

2

If you only have 1 primary shard you do not need dfs_query_then_fetch as only one of the shards serve each query.

3

Thanks for your reply.

The situation I wrote was just example.
So, Could I think that "prequery" is excuted for all shards(primary and replicas)?

And is there any problem to get consistent scoring in case of 1 primary shard?
According to the below reference, I just knew that 1 primary shard might also have same issue.
https://www.elastic.co/guide/en/elasticsearch/reference/6.5/consistent-scoring.html#_scores_are_not_reproducible

4

If you only query a single shard your scoring will be consistent. Only a single copy of each shard (primary or replica) is queries so the answer is one.