# Concurrent updates to ElasticSearch while \_reindex is in progress
**URL:** https://discuss.elastic.co/t/concurrent-updates-to-elasticsearch-while-reindex-is-in-progress/118294
**Category:** Elasticsearch
**Created:** [February 3, 2018, 5:06am UTC](https://discuss.elastic.co/t/concurrent-updates-to-elasticsearch-while-reindex-is-in-progress/118294 "2018-02-03T05:06:53Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@ssg](https://discuss.elastic.co/u/ssg)
#### Post date: [February 3, 2018, 5:06am UTC](https://discuss.elastic.co/t/concurrent-updates-to-elasticsearch-while-reindex-is-in-progress/118294/1 "2018-02-03T05:06:53Z")
Hi team,
We have been using this [link](https://www.elastic.co/guide/en/elasticsearch/guide/current/index-aliases.html) as a reference to accommodate any change in the mappings for a field in our index with zero downtime.
**Question** :
Considering the same example taken in the above link, when we reindex the data from
my\_index\_v1 to my\_index\_v2 using [\_reindex](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-reindex.html) API. Does ElasticSearch guarantee that any concurrent updates happening in my\_index\_v1 would make it to my\_index\_v2 for sure?
For example, a document might get updated in my\_index\_v1 before or after it is reindexed by api to my\_index\_v2.
Ultimately, we just need to ensure that while we did not want any downtime for doing any mapping changes (hence did \_reindex using alias and other cool stuff by ES), we also want to ensure that none of the add/update were missed while this huge reindex was in progress, as we are talking about reindexing \>50GB data.
Thanks,
Sandeep
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### Author:  [@warkolm](https://discuss.elastic.co/u/warkolm)
#### Post date: [February 3, 2018, 8:17pm UTC](https://discuss.elastic.co/t/concurrent-updates-to-elasticsearch-while-reindex-is-in-progress/118294/2 "2018-02-03T20:17:57Z")
> [@ssg](#):
>
> Does Elasticsearch guarantee that any concurrent updates happening in my\_index\_v1 would make it to my\_index\_v2 for sure?
> Just like \_update\_by\_query, \_reindex gets a snapshot of the source index
That's from the docs, which means no, it does not. It takes said snapshot and then reindexes based on that. Changes prior to the snapshot are carried across, those after the snapshot - ie when you make the request - will not be processed.
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [March 3, 2018, 8:18pm UTC](https://discuss.elastic.co/t/concurrent-updates-to-elasticsearch-while-reindex-is-in-progress/118294/3 "2018-03-03T20:18:01Z")
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