# How the 'Transform API' Works

**URL:** <https://discuss.elastic.co/t/how-the-transform-api-works/327516>\
**Category:** Elasticsearch\
**Tags:** transforms\
**Created:** [March 13, 2023, 4:22am UTC](https://discuss.elastic.co/t/how-the-transform-api-works/327516 "2023-03-13T04:22:03Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![SEUNGHYO](https://avatars.discourse-cdn.com/v4/letter/s/65b543/32.png) [@SEUNGHYO](https://discuss.elastic.co/u/SEUNGHYO)\
**Post date:** [March 13, 2023, 4:22am UTC](https://discuss.elastic.co/t/how-the-transform-api-works/327516/1 "2023-03-13T04:22:03Z")

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Hello.

I was check  
"search \> aggregation (size=0)" and "transform \> pivot \> aggregation ( **\_preview** )"  
I checked that the transform side has much fewer tooks.  
(Same aggs, small size set for simple comparison -\> **There was a noticeable difference.** )

How did you get these results?  
May I know how the transform API works in more detail than refer?  
Or  
Do you think there are related documents?

Thank you!

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**Author:** ![Hendrik\_Muhs](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hendrik_muhs/32/25802_2.png) [@Hendrik\_Muhs](https://discuss.elastic.co/u/Hendrik_Muhs)\
**Post date:** [March 13, 2023, 2:36pm UTC](https://discuss.elastic.co/t/how-the-transform-api-works/327516/2 "2023-03-13T14:36:44Z")

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Hi,

transform uses Composite aggregation underneath, wrapped in a search call. There shouldn't be a significant performance difference between a transform preview call or a search. Both calls get executed with the same priority and use the same threadpool.

The [documentation](https://www.elastic.co/guide/en/elasticsearch/reference/current/transform-overview.html) has more information and also explains some inner details like when to use transform vs. something else, checkpointing ans scale considerations.

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<div class="post-metadata">

**Author:** ![SEUNGHYO](https://avatars.discourse-cdn.com/v4/letter/s/65b543/32.png) [@SEUNGHYO](https://discuss.elastic.co/u/SEUNGHYO)\
**Post date:** [March 14, 2023, 1:00am UTC](https://discuss.elastic.co/t/how-the-transform-api-works/327516/3 "2023-03-14T01:00:50Z")

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Thank you for your exact answer! @Hendrik_Muhs

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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:** [April 11, 2023, 1:00am UTC](https://discuss.elastic.co/t/how-the-transform-api-works/327516/4 "2023-04-11T01:00:55Z")

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