# Ask about Heap

**URL:** <https://discuss.elastic.co/t/ask-about-heap/66216>\
**Category:** Elasticsearch\
**Created:** [November 16, 2016, 7:49am UTC](https://discuss.elastic.co/t/ask-about-heap/66216 "2016-11-16T07:49:38Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![nguyenhuukhoinw](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/nguyenhuukhoinw/32/13161_2.png) [@nguyenhuukhoinw](https://discuss.elastic.co/u/nguyenhuukhoinw)\
**Post date:** [November 16, 2016, 7:49am UTC](https://discuss.elastic.co/t/ask-about-heap/66216/1 "2016-11-16T07:49:38Z")

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I read ES document and it recommend that we should set under 50% of memory. However, what happen if ES use more than this amount? And how can we know if ES need more memory? Thank you!

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**Author:** ![rusty](https://avatars.discourse-cdn.com/v4/letter/r/f17d59/32.png) [@rusty](https://discuss.elastic.co/u/rusty)\
**Post date:** [November 17, 2016, 8:27am UTC](https://discuss.elastic.co/t/ask-about-heap/66216/2 "2016-11-17T08:27:47Z")

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In general you should expect search performance degradation or if give ES to much heap OS may kill ES process (OOM killer).  
IMHO the main reason to keep RAM 50/50 is the OS file cache, where hot file blocks accessed by search keeps and can be reused from RAM. If you give ES more memory you'll get much more read I/O from disks. Another pitfall is that you can move system into swap and that kills indexing and search performance.

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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:** [December 15, 2016, 8:27am UTC](https://discuss.elastic.co/t/ask-about-heap/66216/3 "2016-12-15T08:27:55Z")

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Closed on December 15, 2016, 8:27am UTC

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