# Why returning many records with no fields (only IDs) is CPU intensive?

**URL:** <https://discuss.elastic.co/t/why-returning-many-records-with-no-fields-only-ids-is-cpu-intensive/132311>\
**Category:** Elasticsearch\
**Created:** [May 17, 2018, 10:40am UTC](https://discuss.elastic.co/t/why-returning-many-records-with-no-fields-only-ids-is-cpu-intensive/132311 "2018-05-17T10:40:08Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![aliostad](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/aliostad/32/4046_2.png) [@aliostad](https://discuss.elastic.co/u/aliostad)\
**Post date:** [May 17, 2018, 10:40am UTC](https://discuss.elastic.co/t/why-returning-many-records-with-no-fields-only-ids-is-cpu-intensive/132311/1 "2018-05-17T10:40:08Z")

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Hi,

I have been trying to use Elasticsearch for some simple filtering for example for an index with 100K records, return all matching a criteria (using as `terms` query).

When the number of records matching goes above 1K, CPU completely goes bonkers and search becomes very expensive. I do not return any field data, only the ID is enough for me yet it is still expensive.

I cannot use pagination since I need all such data to further process and re-order.

Doing something similar for example in SQL is trivial. I know there is no comparison but would like to understand if I am doing something completely wrong or this is essentially a limitation in Lucene-based indices.

Document size: ~ 4-20KB  
Cluster: 3x beefy machines with 8 cores and 56GB RAM and striped SSDs.

Thanks  
Ali

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**Author:** ![RahulD](https://avatars.discourse-cdn.com/v4/letter/r/da6949/32.png) [@RahulD](https://discuss.elastic.co/u/RahulD)\
**Post date:** [May 17, 2018, 10:53am UTC](https://discuss.elastic.co/t/why-returning-many-records-with-no-fields-only-ids-is-cpu-intensive/132311/2 "2018-05-17T10:53:39Z")

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What is your cluster configuration? And what is the size of each document?

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<div class="post-metadata">

**Author:** ![aliostad](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/aliostad/32/4046_2.png) [@aliostad](https://discuss.elastic.co/u/aliostad)\
**Post date:** [May 17, 2018, 10:54am UTC](https://discuss.elastic.co/t/why-returning-many-records-with-no-fields-only-ids-is-cpu-intensive/132311/3 "2018-05-17T10:54:29Z")

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I am updating the question.

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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:** [June 14, 2018, 10:54am UTC](https://discuss.elastic.co/t/why-returning-many-records-with-no-fields-only-ids-is-cpu-intensive/132311/4 "2018-06-14T10:54:30Z")

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Closed on June 14, 2018, 10:54am UTC

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