Quorum, consistency and datacenter awareness


(HubertChang) #1

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.

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(Shay Banon) #2

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
.

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 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
Sent from the ElasticSearch Users mailing list archive at Nabble.com.


(system) #3