# For any 1.2.0 users - You will want to read this

**URL:** <https://discuss.elastic.co/t/for-any-1-2-0-users-you-will-want-to-read-this/17951>\
**Category:** Elasticsearch\
**Created:** [June 6, 2014, 10:36am UTC](https://discuss.elastic.co/t/for-any-1-2-0-users-you-will-want-to-read-this/17951 "2014-06-06T10:36:33Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\
**Post date:** [June 6, 2014, 10:36am UTC](https://discuss.elastic.co/t/for-any-1-2-0-users-you-will-want-to-read-this/17951/1 "2014-06-06T10:36:33Z")

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> **[Elasticsearch Platform — Find real-time answers at scale](https://www.elastic.co)**
>
> Power insights and outcomes with the Elasticsearch Platform and AI. See into your data and find answers that matter with enterprise solutions designed to help you build, observe, and protect. Try Elasticsearch free today.

> In the 1.2.1 release we fixed a routing bug that had been introduced in  
> the 1.2.0 release. This was described in the 1.2.1 blog post. The contents  
> of this post apply only to users that ran 1.2.0.

Before we can discuss the tool we developed to help fix damage from the

> bug, we have to understand the problem the bug created. When Elasticsearch  
> stores a document it has to decide which shard to put the document in. It  
> does this by computing a hash of the document’s “UID”, which is by default  
> the type#id tuple of the document. Elasticsearch then uses that hash modulo  
> the number of shards to pick a shard. We have to make sure that this hash  
> function works the same across different versions of Elasticsearch. If it  
> doesn’t, version X could expect to find a given document in shard 1 and  
> version X+1 could expect the same document in shard 2. In this case,  
> version X+1 could not directly get the document if it were indexed while  
> running version X.

Regards,  
Mark Walkom

Infrastructure Engineer  
Campaign Monitor  
email: [markw@campaignmonitor.com](mailto:markw@campaignmonitor.com)  
web: [www.campaignmonitor.com](http://www.campaignmonitor.com)

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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:** [July 6, 2017, 1:24am UTC](https://discuss.elastic.co/t/for-any-1-2-0-users-you-will-want-to-read-this/17951/2 "2017-07-06T01:24:11Z")

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Closed on July 6, 2017, 1:24am UTC