Replica allocation concurrent setting

Elastic Stack Elasticsearch
1

Does anybody know what the replica concurrent setting is?

I just set the number_of_replicas from 0 to 1 in a production environment with the below settings:
cluster.routing.allocation.cluster_concurrent_rebalance": "10"
cluster.routing.allocation.node_concurrent_recoveries": "2"

I expected there to be a max 10 replica shards allocation, but instead, there were almost 100 shard allocation tasks triggered which caused severe
impact on the online search, and I want to know the exact settings for replica allocation.

thanks.

2

See the docs for this setting, particularly:

Increasing this setting may cause the cluster to use additional resources moving shards between nodes, so we generally do not recommend adjusting this setting from its default of 2 .

3

yeah, I have learned the lesson,
but I am still confused about why the concurrent allocation tasks were not as expected max 10

4

I'm not sure, but cluster_concurrent_rebalance only limits the number of rebalancing shard movements in the cluster, there are lots of other reasons for shard allocations. Could you share the output from GET _recovery from the time of the problem?

5

hmmm, sorry, I am afraid I can't, cause there is sensitive information can't be shared.

Actually, I just want to know what are the related concurrent settings for replica shards allocation

6

cluster.routing.allocation.node_concurrent_recoveries limits the number of replicas recovering on a node at once.

7

Got it, thank you so much.