# Modifying default \_id field
**URL:** https://discuss.elastic.co/t/modifying-default-id-field/186479
**Category:** Elasticsearch
**Created:** [June 19, 2019, 1:53pm UTC](https://discuss.elastic.co/t/modifying-default-id-field/186479 "2019-06-19T13:53:29Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Karlos](https://discuss.elastic.co/u/Karlos)
#### Post date: [June 19, 2019, 1:53pm UTC](https://discuss.elastic.co/t/modifying-default-id-field/186479/1 "2019-06-19T13:53:30Z")
Hello,
We are working in an Index system with Elasticsearch.ยก, and we would like to have our own \_id fields, using a unique identifier obtained from the document to be inserted, so Elasticsearch drops a new insert in case this \_id is already present in the system.
Roughly a single request unicity check, where the insert just fails to avoid duplication.
My question is, are we loosing performance at Elasticsearch level using our own crafted \_id field?
Is the Index keeping up its performance in resharding operations?
Thanks for any advice.
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### Author:  [@Christian\_Dahlqvist](https://discuss.elastic.co/u/Christian_Dahlqvist)
#### Post date: [June 19, 2019, 2:00pm UTC](https://discuss.elastic.co/t/modifying-default-id-field/186479/2 "2019-06-19T14:00:08Z")
Have a look at [this blog post](https://www.elastic.co/blog/efficient-duplicate-prevention-for-event-based-data-in-elasticsearch).
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 17, 2019, 2:00pm UTC](https://discuss.elastic.co/t/modifying-default-id-field/186479/3 "2019-07-17T14:00:12Z")
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