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From "Ajay Jadhav (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18477) Umbrella JIRA for HBase Read Replica clusters
Date Fri, 25 Aug 2017 21:59:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16142298#comment-16142298
] 

Ajay Jadhav commented on HBASE-18477:
-------------------------------------

[~ashish singhi]:
1. The main intention of having the read-replica feature was to provide HA in case one of
the AZ goes down. For now, it is up to the
client to decide which cluster to connect to. Having a load balancer in front of the active
clusters which tracks the health of each one
could be something we can think about in future work.

2 & 3. The hbase-site.xml for a read-replica will have this key set- "hbase.emr.readreplica.enabled":"true"
But apart from that, doing this programmatically involves catching the readonly exception.
IMO I think since the client always know which cluster they are talking too, providing a programmatic
way seems unnecessary.
Let me know what is your concern here.

Sure, I'll update the documentation.



> Umbrella JIRA for HBase Read Replica clusters
> ---------------------------------------------
>
>                 Key: HBASE-18477
>                 URL: https://issues.apache.org/jira/browse/HBASE-18477
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: Zach York
>            Assignee: Ajay Jadhav
>         Attachments: HBase Read-Replica Clusters Scope doc.docx, HBase Read-Replica Clusters
Scope doc.pdf, HBase Read-Replica Clusters Scope doc_v2.docx
>
>
> Recently, changes (such as HBASE-17437) have unblocked HBase to run with a root directory
external to the cluster (such as in Amazon S3). This means that the data is stored outside
of the cluster and can be accessible after the cluster has been terminated. One use case that
is often asked about is pointing multiple clusters to one root directory (sharing the data)
to have read resiliency in the case of a cluster failure.
>  
> This JIRA is an umbrella JIRA to contain all the tasks necessary to create a read-replica
HBase cluster that is pointed at the same root directory.
>  
> This requires making the Read-Replica cluster Read-Only (no metadata operation or data
operations).
> Separating the hbase:meta table for each cluster (Otherwise HBase gets confused with
multiple clusters trying to update the meta table with their ip addresses)
> Adding refresh functionality for the meta table to ensure new metadata is picked up on
the read replica cluster.
> Adding refresh functionality for HFiles for a given table to ensure new data is picked
up on the read replica cluster.
>  
> This can be used with any existing cluster that is backed by an external filesystem.
>  
> Please note that this feature is still quite manual (with the potential for automation
later).
>  
> More information on this particular feature can be found here: https://aws.amazon.com/blogs/big-data/setting-up-read-replica-clusters-with-hbase-on-amazon-s3/



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