# Rollup API Autogenerated Index Strategy

**URL:** <https://discuss.elastic.co/t/rollup-api-autogenerated-index-strategy/140740>\
**Category:** Elasticsearch\
**Created:** [July 19, 2018, 1:31pm UTC](https://discuss.elastic.co/t/rollup-api-autogenerated-index-strategy/140740 "2018-07-19T13:31:51Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Domenico\_Raimondi](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/domenico_raimondi/32/28631_2.png) [@Domenico\_Raimondi](https://discuss.elastic.co/u/Domenico_Raimondi)\
**Post date:** [July 19, 2018, 1:31pm UTC](https://discuss.elastic.co/t/rollup-api-autogenerated-index-strategy/140740/1 "2018-07-19T13:31:51Z")

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Hello,

In my team, we've been enthusiastically using the new Rollup API. It provides the functionality that we were waiting for!

However, once we started using it, we noticed that the autogenerated \_id for our new rollup index is a random unsigned 32bit integer. This is different than the autogenerated ID strategy that is indicated in [this page](https://www.elastic.co/guide/en/elasticsearch/guide/current/index-doc.html#_autogenerating_ids).

We're worried that the new Rollup index that is generated would run into the [Birthday Paradox](https://en.wikipedia.org/wiki/Birthday_problem) problem, and thus possibly overwrite documents.

Could someone please explain the autogenerated index strategy of Rollup indexes?

Thank you and best regards,  
Dom

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**Author:** ![Luca\_Belluccini](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/luca_belluccini/32/33239_2.png) [@Luca\_Belluccini](https://discuss.elastic.co/u/Luca_Belluccini)\
**Post date:** [July 26, 2018, 6:20am UTC](https://discuss.elastic.co/t/rollup-api-autogenerated-index-strategy/140740/2 "2018-07-26T06:20:01Z")

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Hello Domenico,  
the `_id` is actually a `32bit CRC` at the moment.  
It was not possible to use the standard `ES GUID` as those ids must be deterministic, but it can improved.  
An [issue](https://github.com/elastic/elasticsearch/issues/32372) has been published for this reason.  
Remember the Rollup API is **still experimental**.

Hope it helps!

Luca

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**Author:** ![Domenico\_Raimondi](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/domenico_raimondi/32/28631_2.png) [@Domenico\_Raimondi](https://discuss.elastic.co/u/Domenico_Raimondi)\
**Post date:** [July 26, 2018, 8:48am UTC](https://discuss.elastic.co/t/rollup-api-autogenerated-index-strategy/140740/3 "2018-07-26T08:48:20Z")

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Thank you @Luca_Belluccini for pushing to get this issue tracked openly.

Indeed in my team we have indices that, when rolled up, can indeed pass over the 200k barrier. As such, Rollup is not usable in its current state until we know for sure that we won't generate any collisions.

We eagerly await a resolution! 🙂

Best Regards,  
Dom

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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:** [August 23, 2018, 8:48am UTC](https://discuss.elastic.co/t/rollup-api-autogenerated-index-strategy/140740/4 "2018-08-23T08:48:24Z")

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Closed on August 23, 2018, 8:48am UTC

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