# Query phase behavior

**URL:** <https://discuss.elastic.co/t/query-phase-behavior/208729>\
**Category:** Elasticsearch\
**Created:** [November 20, 2019, 3:25pm UTC](https://discuss.elastic.co/t/query-phase-behavior/208729 "2019-11-20T15:25:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Loris](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/loris/32/45281_2.png) [@Loris](https://discuss.elastic.co/u/Loris)\
**Post date:** [November 20, 2019, 3:25pm UTC](https://discuss.elastic.co/t/query-phase-behavior/208729/1 "2019-11-20T15:25:58Z")

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Hi,  
I have a doubt about the behavior of the Coordinating Node during the query phase: is there a specific criteria which leads it to choose between a primary or a replica of each shard?  
Considering the following scenario:

HOST #0  
Coordinating Node

HOST #1  
P1  
P4  
R3

HOST #2  
P2  
R0  
R1

HOST #3  
P0  
P3  
R2  
R4

What should be the reason to make him choose to query P4 instead of R4?  
Thanks,

Loris

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<div class="post-metadata">

**Author:** ![spinscale](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/spinscale/32/25011_2.png) [@spinscale](https://discuss.elastic.co/u/spinscale)\
**Post date:** [November 21, 2019, 12:14pm UTC](https://discuss.elastic.co/t/query-phase-behavior/208729/2 "2019-11-21T12:14:49Z")

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The mechanism to pick the shards is called Adaptive Replica Selection. See [https://www.elastic.co/guide/en/elasticsearch/reference/7.4/search.html#search-adaptive-replica](https://www.elastic.co/guide/en/elasticsearch/reference/7.4/search.html#search-adaptive-replica)

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [December 19, 2019, 12:14pm UTC](https://discuss.elastic.co/t/query-phase-behavior/208729/3 "2019-12-19T12:14:49Z")

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