# Quorum, consistency and datacenter awareness

**URL:** <https://discuss.elastic.co/t/quorum-consistency-and-datacenter-awareness/2888>\
**Category:** Elasticsearch\
**Created:** [April 4, 2010, 4:59pm UTC](https://discuss.elastic.co/t/quorum-consistency-and-datacenter-awareness/2888 "2010-04-04T16:59:48Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![HubertChang](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hubertchang/32/3352_2.png) [@HubertChang](https://discuss.elastic.co/u/HubertChang)\
**Post date:** [April 4, 2010, 4:59pm UTC](https://discuss.elastic.co/t/quorum-consistency-and-datacenter-awareness/2888/1 "2010-04-04T16:59:48Z")

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## ElasticSearch works in the cluster. Is there a quorum concept? If the replication factor is 2 or 3 and one replication fails, is the content still available? Is there a param to read from \_all\_replications and read from \_one\_replication to maintain the consitency? Will the replication be datacenter awared in the future? Thanks.

View this message in context: [http://n3.nabble.com/quorum-consistency-and-datacenter-awareness-tp696373p696373.html](http://n3.nabble.com/quorum-consistency-and-datacenter-awareness-tp696373p696373.html)  
Sent from the ElasticSearch Users mailing list archive at [Nabble.com](http://Nabble.com).

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**Author:** ![kimchy](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/kimchy/32/44952_2.png) [@kimchy](https://discuss.elastic.co/u/kimchy)\
**Post date:** [April 4, 2010, 6:25pm UTC](https://discuss.elastic.co/t/quorum-consistency-and-datacenter-awareness/2888/2 "2010-04-04T18:25:39Z")

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Date center has been discussed here:  
[http://groups.google.com/a/elasticsearch.com/group/users/browse\_thread/thread/44e8e96420d78201/0275c454ae80ad01?lnk=gst&q=data+center#0275c454ae80ad01](http://groups.google.com/a/elasticsearch.com/group/users/browse_thread/thread/44e8e96420d78201/0275c454ae80ad01?lnk=gst&q=data+center#0275c454ae80ad01)  
.

ElaticSearch clustering module is different than cassandra and other dynamo  
based systems. You don't have to read from all/quorum replicas in order to  
maintain consistency. When something is indexed, it is indexed on a primary  
shard and then replicated to all its replicas synchronously (if you have  
more than one replica, it is done in parallel using async io).

Note, that elasticsearch provides near real time for indexed documents to be  
visible when searching/getting them. But, if (when) it provides real time  
support, then once you indexed, it will be provided immediately and no need  
for quorum based reads.

When doing a read / search, one of the replicas is chosen and the reads is  
done from it. Search is never done on more than one replica of the same  
shard. This gives you better performance and better read/search scalability  
just by increasing the number of replicas.

-shay.banon

On Sun, Apr 4, 2010 at 7:59 PM, HubertChang [huixiu@gmail.com](mailto:huixiu@gmail.com) wrote:

> Elasticsearch works in the cluster.  
> Is there a quorum concept? If the replication factor is 2 or 3 and one  
> replication fails, is the content still available

Is there a param to read from \_all\_replications and read from

> \_one\_replication to maintain the consitency?

Will the replication be datacenter awared in the future?

> ## Thanks.
> 
> View this message in context:  
> [http://n3.nabble.com/quorum-consistency-and-datacenter-awareness-tp696373p696373.html](http://n3.nabble.com/quorum-consistency-and-datacenter-awareness-tp696373p696373.html)  
> Sent from the Elasticsearch Users mailing list archive at [Nabble.com](http://Nabble.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, 4:24am UTC](https://discuss.elastic.co/t/quorum-consistency-and-datacenter-awareness/2888/3 "2017-07-06T04:24:51Z")

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