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[DOCS] Clarify Recovery Settings for Shard Relocation (#40329)
* Clarify that peer recovery settings apply to shard relocation * Fix awkward wording of 1st sentence * [DOCS] Remove snapshot recovery reference. Call out link to [[cat-recovery]]. Separate expert settings.
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[[recovery]] | ||
=== Indices Recovery | ||
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<<cat-recovery,Peer recovery>> is the process used to build a new copy of a | ||
shard on a node by copying data from the primary. {es} uses this peer recovery | ||
process to rebuild shard copies that were lost if a node has failed, and uses | ||
the same process when migrating a shard copy between nodes to rebalance the | ||
cluster or to honor any changes to the <<modules-cluster,shard allocation | ||
settings>>. | ||
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The following _expert_ setting can be set to manage the resources consumed by | ||
peer recoveries: | ||
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`indices.recovery.max_bytes_per_sec`:: | ||
Limits the total inbound and outbound peer recovery traffic on each node. | ||
Since this limit applies on each node, but there may be many nodes | ||
performing peer recoveries concurrently, the total amount of peer recovery | ||
traffic within a cluster may be much higher than this limit. If you set | ||
this limit too high then there is a risk that ongoing peer recoveries will | ||
consume an excess of bandwidth (or other resources) which could destabilize | ||
the cluster. Defaults to `40mb`. | ||
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`indices.recovery.max_concurrent_file_chunks`:: | ||
Controls the number of file chunk requests that can be sent in parallel per recovery. | ||
As multiple recoveries are already running in parallel (controlled by | ||
cluster.routing.allocation.node_concurrent_recoveries), increasing this expert-level | ||
setting might only help in situations where peer recovery of a single shard is not | ||
reaching the total inbound and outbound peer recovery traffic as configured by | ||
indices.recovery.max_bytes_per_sec, but is CPU-bound instead, typically when using | ||
transport-level security or compression. Defaults to `2`. | ||
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This setting can be dynamically updated on a live cluster with the | ||
<<cluster-update-settings,cluster-update-settings>> API. | ||
Peer recovery syncs data from a primary shard to a new or | ||
existing shard copy. | ||
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Peer recovery automatically occurs when {es}: | ||
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* Recreates a shard lost during node failure | ||
* Relocates a shard to another node due to a cluster rebalance or changes to the | ||
<<modules-cluster, shard allocation settings>> | ||
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You can view a list of in-progress and completed recoveries using the | ||
<<cat-recovery, cat recovery API>>. | ||
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[float] | ||
==== Peer recovery settings | ||
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`indices.recovery.max_bytes_per_sec` (<<cluster-update-settings,Dynamic>>):: | ||
Limits total inbound and outbound recovery traffic for each node. | ||
Defaults to `40mb`. | ||
+ | ||
This limit applies to nodes only. If multiple nodes in a cluster perform | ||
recoveries at the same time, the cluster's total recovery traffic may exceed | ||
this limit. | ||
+ | ||
If this limit is too high, ongoing recoveries may consume an excess | ||
of bandwidth and other resources, which can destabilize the cluster. | ||
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[float] | ||
==== Expert peer recovery settings | ||
You can use the following _expert_ setting to manage resources for peer | ||
recoveries. | ||
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`indices.recovery.max_concurrent_file_chunks` (<<cluster-update-settings,Dynamic>>, Expert):: | ||
Number of file chunk requests sent in parallel for each recovery. Defaults to | ||
`2`. | ||
+ | ||
You can increase the value of this setting when the recovery of a single shard | ||
is not reaching the traffic limit set by `indices.recovery.max_bytes_per_sec`. |