# What algorithm is ElasticSearch create Document \_Id based on?Could somebody answer me，plz

**URL:** <https://discuss.elastic.co/t/what-algorithm-is-elasticsearch-create-document-id-based-on-could-somebody-answer-me-plz/166317>\
**Category:** Elasticsearch\
**Created:** [January 30, 2019, 9:24am UTC](https://discuss.elastic.co/t/what-algorithm-is-elasticsearch-create-document-id-based-on-could-somebody-answer-me-plz/166317 "2019-01-30T09:24:39Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![ennian001](https://avatars.discourse-cdn.com/v4/letter/e/779978/32.png) [@ennian001](https://discuss.elastic.co/u/ennian001)\
**Post date:** [January 30, 2019, 9:24am UTC](https://discuss.elastic.co/t/what-algorithm-is-elasticsearch-create-document-id-based-on-could-somebody-answer-me-plz/166317/1 "2019-01-30T09:24:39Z")

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![QQ%E5%9B%BE%E7%89%8720190130165644](https://us1.discourse-cdn.com/elastic/original/3X/a/5/a52ad16d5ddb011e1e2914496d3a5b1cf777bfd9.png)  
the \_id is UUID?  
If I want to specify my own ID, according to the formula（shard = hash(routing) % number\_of\_primary\_shards）, will it result in uneven sharding?  
I'm confused about this. Can someone help me? plz, i'd really appreciate it .

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**Author:** ![DavidTurner](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/davidturner/32/22453_2.png) [@DavidTurner](https://discuss.elastic.co/u/DavidTurner)\
**Post date:** [January 30, 2019, 10:27am UTC](https://discuss.elastic.co/t/what-algorithm-is-elasticsearch-create-document-id-based-on-could-somebody-answer-me-plz/166317/2 "2019-01-30T10:27:56Z")

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The code that generates auto-generated IDs is below.

> <https://github.com/elastic/elasticsearch/blob/99f88f15c5febbca2d13b5b5fda27b844153bf1a/server/src/main/java/org/elasticsearch/common/TimeBasedUUIDGenerator.java#L80-L118>

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**Author:** ![ennian001](https://avatars.discourse-cdn.com/v4/letter/e/779978/32.png) [@ennian001](https://discuss.elastic.co/u/ennian001)\
**Post date:** [January 31, 2019, 2:56am UTC](https://discuss.elastic.co/t/what-algorithm-is-elasticsearch-create-document-id-based-on-could-somebody-answer-me-plz/166317/3 "2019-01-31T02:56:37Z")

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Thank you , you are very kind....you're really help me a lot...😚😚😚😚😚😚😚

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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:** [February 28, 2019, 3:08am UTC](https://discuss.elastic.co/t/what-algorithm-is-elasticsearch-create-document-id-based-on-could-somebody-answer-me-plz/166317/4 "2019-02-28T03:08:20Z")

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