# What happens when decommission a node?

**URL:** <https://discuss.elastic.co/t/what-happens-when-decommission-a-node/260938>\
**Category:** Elasticsearch\
**Created:** [January 13, 2021, 6:25am UTC](https://discuss.elastic.co/t/what-happens-when-decommission-a-node/260938 "2021-01-13T06:25:35Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![linkerc](https://avatars.discourse-cdn.com/v4/letter/l/13edae/32.png) [@linkerc](https://discuss.elastic.co/u/linkerc)\
**Post date:** [January 13, 2021, 6:25am UTC](https://discuss.elastic.co/t/what-happens-when-decommission-a-node/260938/1 "2021-01-13T06:25:35Z")

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I just decommissioned a node from my cluster. I noticed there are many threads (15-20) doing the shard relocation, which is great.  
After about 30 minutes, the rebalancing threads dropped down to 3, which is my cluster setting for  
"node\_concurrent\_recoveries".  
The online document states:

> `cluster.routing.allocation.cluster_concurrent_rebalance`
> 
> Allow to control how many concurrent shard rebalances are allowed cluster wide. Defaults to `2` . Note that this setting only controls the number of concurrent shard relocations due to imbalances in the cluster. This setting does not limit shard relocations due to [allocation filtering](https://www.elastic.co/guide/en/elasticsearch/reference/7.6/allocation-filtering.html) or [forced awareness](https://www.elastic.co/guide/en/elasticsearch/reference/7.6/allocation-awareness.html#forced-awareness).

Why does the concurrent relocation threads dropped? Is this by design? It makes the decommission process longer IMO. Since "allocation filtering" doesn't have to follow the setting anyway.

I believe during the first 30 min, there are lots of activities between nodes (not just the decommissioned node). Which suggests the cluster is using backup/primary to rebalance (many to many transfer).  
But after 30 minutes or so, it becomes 1 to many transfer.

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [February 10, 2021, 6:25am UTC](https://discuss.elastic.co/t/what-happens-when-decommission-a-node/260938/2 "2021-02-10T06:25:49Z")

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