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Chao Sun commented on HDFS-12975: --------------------------------- Thanks [~shv] for taking a look! I've fixed the changes for the 1) and 3), and currently is working on a way to let observer participate in failover. There are some complexities: According to the design, during failover we want to choose SBN over Observer if the former is available. Therefore, the logic in {{ZKFailoverController}} will need to change. First, for graceful failover, I'm thinking about associating each target with a flag indicating whether it is a "preferred" target (e.g., SBN). In {{ZKFailoverController::doGracefulFailover()}} we will then check the flag of the local target against all the flags of the other nodes, and determine the action (e.g., when local target is non-preferred and there exists at least one preferred target in other nodes, quit the election). Second, for the case of "ungraceful" failover, such as ANN crash, it seems more difficult. The current mechanism is to haveĀ all the available candidates to compete for the ZK lock, so there is no way for them to communicate and coordinate such that SBN will be preferred. I'll continue to look into this. But let me know if you have any good suggestions. > Changes to the NameNode to support reads from standby > ----------------------------------------------------- > > Key: HDFS-12975 > URL: https://issues.apache.org/jira/browse/HDFS-12975 > Project: Hadoop HDFS > Issue Type: Sub-task > Components: namenode > Reporter: Konstantin Shvachko > Assignee: Chao Sun > Priority: Major > Attachments: HDFS-12975.000.patch > > > In order to support reads from standby NameNode needs changes to add Observer > role, turn off checkpointing and such. -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org