# Unexpected high memory usage in Elasticsearch cluster – looking for optimization advice
**URL:** https://discuss.elastic.co/t/unexpected-high-memory-usage-in-elasticsearch-cluster-looking-for-optimization-advice/384629
**Category:** Elasticsearch
**Created:** [January 19, 2026, 5:35pm UTC](https://discuss.elastic.co/t/unexpected-high-memory-usage-in-elasticsearch-cluster-looking-for-optimization-advice/384629 "2026-01-19T17:35:11Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@jimmykalru](https://discuss.elastic.co/u/jimmykalru)
#### Post date: [January 19, 2026, 5:35pm UTC](https://discuss.elastic.co/t/unexpected-high-memory-usage-in-elasticsearch-cluster-looking-for-optimization-advice/384629/1 "2026-01-19T17:35:11Z")
I’m running an Elasticsearch cluster in a production environment and recently noticed **consistently high memory usage** across all data nodes. Even during periods of low query activity[,](https://riyadhmetrosa.com) heap usage remains elevated and occasionally triggers long GC pauses.
**Environment details:**
- Elasticsearch version: 8.x
- Cluster size: 3 data nodes, 1 master
- Each data node: 16 GB RAM, heap set to 8 GB
- Primary use-case: log ingestion and search (via Filebeat + Kibana)
**Symptoms:**
- Heap usage rarely drops below ~75%
- Occasional slow searches during peak ingestion
- GC logs show frequent old-gen collections
**What I’ve checked so far:**
- No unusually large aggregations running
- Shard count appears reasonable
- Fielddata cache not heavily used
- Circuit breakers not being triggered
I’d appreciate any guidance on:
- Common causes of sustained high heap usage
- Recommended tuning steps or metrics I should inspect
- Whether this could be related to segment merging or mapping design
I’m happy to share additional logs or stats if needed.
---
### Author:  [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)
#### Post date: [January 19, 2026, 5:55pm UTC](https://discuss.elastic.co/t/unexpected-high-memory-usage-in-elasticsearch-cluster-looking-for-optimization-advice/384629/2 "2026-01-19T17:55:39Z")
> [@jimmykalru](#):
>
> Elasticsearch version: 8.x
Exactly which version are you using?
> [@jimmykalru](#):
>
> Cluster size: 3 data nodes, 1 master
Having a single master node in a cluster is not recommended as you have limited resiliency and no high availability. You should always aim to have 3 master eligible nodes in any cluster larger than a single node.
> [@jimmykalru](#):
>
> Each data node: 16 GB RAM, heap set to 8 GB
How much disk space does the node have? What type of storage are you using?
What is the full output of the [cluster stats API](https://www.elastic.co/guide/en/elasticsearch/reference/8.19/cluster-stats.html)?
> [@jimmykalru](#):
>
> Heap usage rarely drops below ~75%
This often indicates that you either need to improve the efficiency of the data stored in Elasticsearch or increase RAM and heap.
> [@jimmykalru](#):
>
> Occasional slow searches during peak ingestion
This can be an indication of slow storage, which is why I asked about this earlier. Maybe run `iostat -x` on the nodes during heavy load to see exactly what is going on.
> [@jimmykalru](#):
>
> - GC logs show frequent old-gen collections
Do you have swapping enabled? If not, is the cluster deployed on VMs that may not have enough RAM and use swapping behind the scenes?
> [@jimmykalru](#):
>
> Shard count appears reasonable
What is your definition of reasonable? The output of the API I linked to earlier will provide stats around this as well as an indication of the type of mappings used.