# Fastest way to reindex from 2.3 to 6.4

**URL:** <https://discuss.elastic.co/t/fastest-way-to-reindex-from-2-3-to-6-4/148930>\
**Category:** Elasticsearch\
**Created:** [September 18, 2018, 6:51am UTC](https://discuss.elastic.co/t/fastest-way-to-reindex-from-2-3-to-6-4/148930 "2018-09-18T06:51:23Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![hamid\_bayat](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hamid_bayat/32/74056_2.png) [@hamid\_bayat](https://discuss.elastic.co/u/hamid_bayat)\
**Post date:** [September 18, 2018, 6:51am UTC](https://discuss.elastic.co/t/fastest-way-to-reindex-from-2-3-to-6-4/148930/1 "2018-09-18T06:51:23Z")

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Hi  
we have 300TB indices 2.3.5 and we want to upgrade to elasticsearch 6.3.

we set refresh interval to -1  
replica to 0  
request\_per\_second to -1  
and we run 10 remote reindex API on 3 coordinator node.  
our tests show that it will be converted over 3 month.  
how can we decrease the reindex time?  
any suggestion will be appreciated.

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**Author:** ![zqc0512](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/zqc0512/32/32141_2.png) [@zqc0512](https://discuss.elastic.co/u/zqc0512)\
**Post date:** [September 18, 2018, 6:55am UTC](https://discuss.elastic.co/t/fastest-way-to-reindex-from-2-3-to-6-4/148930/2 "2018-09-18T06:55:43Z")

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not use the default api.  
use java client search the es 2.3 data and use bulk to write to the new 6.3 es cluster

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<div class="post-metadata">

**Author:** ![hamid\_bayat](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hamid_bayat/32/74056_2.png) [@hamid\_bayat](https://discuss.elastic.co/u/hamid_bayat)\
**Post date:** [September 25, 2018, 11:34am UTC](https://discuss.elastic.co/t/fastest-way-to-reindex-from-2-3-to-6-4/148930/3 "2018-09-25T11:34:50Z")

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we increase the bulk size and had better performance.

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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:** [October 23, 2018, 11:34am UTC](https://discuss.elastic.co/t/fastest-way-to-reindex-from-2-3-to-6-4/148930/4 "2018-10-23T11:34:54Z")

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