---
title: Unbalanced GC ratio
description: Describes what AutoOps detects and surfaces with the Unbalanced GC ratio insight: Garbage collection time is unbalanced between young and old heap generations on the affected node.
url: https://docs-v3-preview.elastic.dev/elastic/autoops-insights/tree/main/elasticsearch/unbalanced_gc_ratio
products:
  - Elastic Cloud Enterprise
  - Elastic Cloud Hosted
  - Elastic Cloud on Kubernetes
  - Elasticsearch
applies_to:
  - Elastic Cloud Hosted: Generally available
  - Elastic Cloud on Kubernetes: Generally available
  - Elastic Cloud Enterprise: Generally available
  - Self-managed Elastic deployments: Generally available
---

# Unbalanced GC ratio
Garbage collection time is unbalanced between young and old heap generations on the affected node. The node might pause more often while old-generation collections run, which hurts search and indexing responsiveness.
<note>
  For a complete list of insights, refer to [AutoOps insights](https://docs-v3-preview.elastic.dev/elastic/autoops-insights/tree/main/elasticsearch).
</note>


## Insight details


| Field     | Value                       |
|-----------|-----------------------------|
| Component | Elasticsearch               |
| Severity  | Medium                      |
| Scope     | Node                        |
| Domains   | performance, cpu, stability |


## Customization settings

You can customize these settings to adjust when AutoOps detects this event and presents the insight. Refer to [AutoOps event settings](https://docs-v3-preview.elastic.dev/elastic/docs-content/tree/main/deploy-manage/monitor/autoops/ec-autoops-event-settings) for details.
The default customization settings are:

| Setting                                      | Type       | Default |
|----------------------------------------------|------------|---------|
| Delta between old and young GC in percentage | Percentage | `50`    |


## Example: What you might see in AutoOps

The following is an example of what you might see when this insight is triggered. Real insights use live data and links from your deployment or cluster.

### GC ratio between old and young generations is unbalanced on es-data-01


#### What was detected

Old and young GC time shares are unbalanced on `es-data-01` and `es-data-02`. old GC is loading more than young GC.
- Indices with high search activity: `logs-prod-000045`
- Indices with high indexing activity: `logs-prod-000045`


#### Recommendations

<note>
  AutoOps shows different recommendations depending on how their conditions match your deployment or cluster.
</note>

<dropdown title="Balance old and young GC">
  **Condition**: Shown when the gc-old / gc-new ratio diverges by more than 50%.Set `-XX:NewRatio=2` in your JVM options file to tune the ratio between old and young GC, then perform a rolling restart of affected nodes.
</dropdown>

<dropdown title="Increase parallel GC threads">
  **Condition**: Shown when gC load is unbalanced across nodes.Set `-XX:ParallelGCThreads` to the number of available processors on the data node, then restart the node.
</dropdown>

<dropdown title="Enable and review search slow logs">
  **Condition**: Shown when gC load is unbalanced across nodes.Enable search slow logs with the action below, then review the slow log to find expensive queries. See [Slow logs](https://docs-v3-preview.elastic.dev/elastic/docs-content/tree/main/deploy-manage/monitor/logging-configuration/slow-logs) for configuration details.
  ```json

  {
    "index.search.slowlog.threshold.query.warn": "10s",
    "index.search.slowlog.threshold.query.info": "5s",
    "index.search.slowlog.threshold.query.debug": "2s",
    "index.search.slowlog.threshold.query.trace": "500ms",
    "index.search.slowlog.threshold.fetch.warn": "1s",
    "index.search.slowlog.threshold.fetch.info": "800ms",
    "index.search.slowlog.threshold.fetch.debug": "500ms",
    "index.search.slowlog.threshold.fetch.trace": "200ms"
  }
  ```

  <note>
    Requires the `manage` index privilege. Requires Elasticsearch 8.0.0 or later. This action changes cluster or index configuration.
  </note>
</dropdown>


#### Background and impact

The JVM frees heap with young-generation and old-generation collectors. Young collections normally run more often and finish quickly. Old collections reclaim longer-lived objects and can pause the node longer when they run.
When the time share between generations diverges sharply, the heavier generation dominates pause time. The node can stop responding more often while old GC completes. Heavy search or indexing on the same node often contributes to the imbalance.

## Guide

[High JVM memory pressure](https://docs-v3-preview.elastic.dev/elastic/docs-content/tree/main/troubleshoot/elasticsearch/high-jvm-memory-pressure)