# Concerns about Dynamic Field Mapping

**URL:** <https://discuss.elastic.co/t/concerns-about-dynamic-field-mapping/205175>\
**Category:** Elasticsearch\
**Created:** [October 25, 2019, 3:42am UTC](https://discuss.elastic.co/t/concerns-about-dynamic-field-mapping/205175 "2019-10-25T03:42:10Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ycydsxy](https://avatars.discourse-cdn.com/v4/letter/y/d26b3c/32.png) [@ycydsxy](https://discuss.elastic.co/u/ycydsxy)\
**Post date:** [October 25, 2019, 3:42am UTC](https://discuss.elastic.co/t/concerns-about-dynamic-field-mapping/205175/1 "2019-10-25T03:42:10Z")

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I'm new to Elastic Search and I read about the feature of dynamic field mapping at [https://www.elastic.co/guide/en/elasticsearch/reference/6.8/dynamic-field-mapping.html](https://www.elastic.co/guide/en/elasticsearch/reference/6.8/dynamic-field-mapping.html).

It's not possible to change an exist field mapping unless you take the REINDEX action. But what will ES do when we just add a new field mapping ( or index a document with new properties)? is this a heavy work for ES when many documents already exist in this index?

Assuming we have 10,000,000 documents in "INDEX\_1". Each of them has a similar structure like:  
{  
"name" : xxx,  
"age": xxx  
}

Now we index a new document:  
{  
"name": "Kevin",  
"age": 22,  
"new field" : "something"  
}

I wonder whether the index action of the new document will affect the existing 10,000,000 document and have a great impact on cluster performance.

Thanks~

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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:** [November 22, 2019, 3:42am UTC](https://discuss.elastic.co/t/concerns-about-dynamic-field-mapping/205175/2 "2019-11-22T03:42:16Z")

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