# What happends when heap\_used\_percent hits 100%?

**URL:** <https://discuss.elastic.co/t/what-happends-when-heap-used-percent-hits-100/42023>\
**Category:** Elasticsearch\
**Created:** [February 17, 2016, 12:10pm UTC](https://discuss.elastic.co/t/what-happends-when-heap-used-percent-hits-100/42023 "2016-02-17T12:10:26Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dynamicscope](https://avatars.discourse-cdn.com/v4/letter/d/e9bcb4/32.png) [@dynamicscope](https://discuss.elastic.co/u/dynamicscope)\
**Post date:** [February 17, 2016, 12:10pm UTC](https://discuss.elastic.co/t/what-happends-when-heap-used-percent-hits-100/42023/1 "2016-02-17T12:10:26Z")

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Hello, ElasticSearch users.  
I'm very new to ElasticSearch and just publish an ElasticSearch cluster.

My first try, without setting ES\_HEAP\_SIZE, gave me OutOfMemory Exception and the cluster lost all the nodes.

Now I've set ES\_HEAP\_SIZE to 50% of total memory (as recommended) and I am currently monitoring node stats.

It looks like heap\_used\_percent grows very quickly. It hit 70% in 6 hours.

So I am worrying about another OOM.

Could anyone tell me what happends when heap\_used\_percent hits 100%?

Thanks.

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**Author:** ![dynamicscope](https://avatars.discourse-cdn.com/v4/letter/d/e9bcb4/32.png) [@dynamicscope](https://discuss.elastic.co/u/dynamicscope)\
**Post date:** [February 17, 2016, 1:02pm UTC](https://discuss.elastic.co/t/what-happends-when-heap-used-percent-hits-100/42023/2 "2016-02-17T13:02:09Z")

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I found a document on it.

> **[Monitoring Individual Nodes | Elasticsearch: The Definitive Guide \[2.x\] |...](https://www.elastic.co/guide/en/elasticsearch/guide/current/_monitoring_individual_nodes.html#_jvm_section)**

It says,

> The heap\_used\_percent metric is a useful number to keep an eye on. Elasticsearch is configured to initiate GCs when the heap reaches 75% full. If your node is consistently \>= 75%, your node is experiencing memory pressure. This is a warning sign that slow GCs may be in your near future.

> If the heap usage is consistently \>=85%, you are in trouble. Heaps over 90–95% are in risk of horrible performance with long 10–30s GCs at best, and out-of-memory (OOM) exceptions at worst.

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**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\
**Post date:** [February 18, 2016, 6:17am UTC](https://discuss.elastic.co/t/what-happends-when-heap-used-percent-hits-100/42023/3 "2016-02-18T06:17:30Z")

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When it hits 100% it'll usually OOM.  
If it is growing too fast then you need to increase the heap, add other nodes to the cluster, or reduce the amount of data in the cluster.

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 5, 2017, 11:15pm UTC](https://discuss.elastic.co/t/what-happends-when-heap-used-percent-hits-100/42023/4 "2017-07-05T23:15:26Z")

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