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https://issues.apache.org/jira/browse/PHOENIX-7493?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jacob Isaac reassigned PHOENIX-7493:
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Assignee: Jacob Isaac
> Graceful Failover with Phoenix HA
> ---------------------------------
>
> Key: PHOENIX-7493
> URL: https://issues.apache.org/jira/browse/PHOENIX-7493
> Project: Phoenix
> Issue Type: Improvement
> Reporter: Kadir Ozdemir
> Assignee: Jacob Isaac
> Priority: Major
>
> Phoenix HA (PHOENIX-6491) suggests a best effort failover process for the
> failover HA policy. The first step is to make both clusters’ roles Standby,
> and then wait for replication to finish (best-effort). The final step is to
> make the other cluster role Active.
> When the cluster role is set to Standby, the dual cluster Phoenix client does
> not allow read/write operations on a standby cluster. This helps drain
> replication data from the previously Active cluster to the previously Standby
> cluster. However, in practice a cluster may receive changes without using the
> Phoenix dual client. For example, data can be inserted through MapReduce jobs
> which do not use the Phoenix JDBC client. Another example is that the
> previously active cluster could be receiving replication data from a third
> cluster.
> This means pausing writes at the Phoenix client is not sufficient for a
> graceful failover operation. Here graceful means consistent failover between
> two healthy clusters. A consistent failover can be achieved only when the
> replication data is completely sent to the soon to-be Active cluster.
> To ensure that all incoming data is paused before the failover event, we need
> to stop writing to the cluster at the server side. To achieve this, a Phoenix
> coprocessor can also maintain and watch cluster role changes and stop writes
> when an Active cluster becomes Standby as the dual Phoenix client does. In
> order to eliminate the ambiguity on which cluster was previously Active, a
> new HA role called ActiveToStandby is introduced. Both Phoenix client and
> server do not allow write operations on an ActiveToStandby cluster.
> With the above changes, graceful failover is achieved by the following steps
> # Change the Active cluster’s role to ActiveToStandby,
> # Wait for the replication data is drained
> # Change the Standby cluster’s role to Active, and the ActiveToStandby
> cluster’s role Standby
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