The indices.recovery.max_concurrent_operations setting in Elasticsearch controls the maximum number of concurrent operations allowed during shard recovery processes. This setting plays a crucial role in managing the resource utilization and performance of the cluster during recovery events.
Description
- Default Value: 1
- Possible Values: Any positive integer
- Recommendation: The optimal value depends on your cluster's hardware capabilities and recovery requirements. Start with the default and increase gradually while monitoring performance.
This setting limits the number of concurrent file operations that can occur during shard recovery. It affects both peer recovery (when shards are recovered from other nodes) and snapshot recovery (when shards are recovered from snapshots).
Example
To change the indices.recovery.max_concurrent_operations setting using the cluster settings API:
PUT _cluster/settings
{
"persistent": {
"indices.recovery.max_concurrent_operations": 4
}
}
Increasing this value can potentially speed up recovery processes by allowing more concurrent operations. However, it also increases the load on the system, particularly on I/O and network resources.
Common Issues and Misuses
- Setting the value too high can lead to excessive resource consumption, potentially impacting the performance of other operations in the cluster.
- Setting the value too low may unnecessarily slow down recovery processes, especially in clusters with powerful hardware.
Do's and Don'ts
- Do monitor system resources (CPU, memory, I/O) when adjusting this setting.
- Do consider the capabilities of your hardware when configuring this setting.
- Don't set this value excessively high without careful testing and monitoring.
- Don't change this setting frequently; find a stable value that works for your cluster.
Frequently Asked Questions
Q: How does this setting differ from indices.recovery.max_bytes_per_sec?
A: While indices.recovery.max_bytes_per_sec limits the bandwidth used for recovery, indices.recovery.max_concurrent_operations limits the number of concurrent file operations. They work together to control different aspects of the recovery process.
Q: Can increasing this setting always improve recovery speed?
A: Not necessarily. While it can potentially speed up recovery, the actual improvement depends on your hardware capabilities and other concurrent activities in the cluster. Increasing it beyond what your system can handle may lead to degraded performance.
Q: Should I adjust this setting differently for SSD vs HDD storage?
A: Yes, SSDs can generally handle more concurrent operations than HDDs. You might be able to set a higher value for SSD-based nodes, but always test and monitor the impact.
Q: How does this setting interact with the number of shards being recovered?
A: This setting applies globally to all recovery operations in the cluster. If you have many shards being recovered simultaneously, a higher value might be beneficial, but it's important to balance this with overall system load.
Q: Can this setting be changed dynamically?
A: Yes, this setting can be changed dynamically using the cluster settings API without requiring a cluster restart. However, changes will only affect new recovery operations, not ones already in progress.
