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From "Todd Lipcon (Resolved) (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HDFS-2603) HA: don't initialize replication queues until entering Active mode
Date Wed, 21 Dec 2011 06:13:30 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2603?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon resolved HDFS-2603.
-------------------------------

    Resolution: Duplicate

This work got incorporated into HDFS-1972
                
> HA: don't initialize replication queues until entering Active mode
> ------------------------------------------------------------------
>
>                 Key: HDFS-2603
>                 URL: https://issues.apache.org/jira/browse/HDFS-2603
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>
> As described in the comments of HDFS-1975:
> 1) Active NN receives setReplication to drop some file's replication from 3 to 1
> 2) It writes OP_SET_REPLICATION to its log, invalidates two replicas, and returns
> 3) The DNs report BLOCK_INVALIDATED back to both the ActiveNN and SBNN.
> 4) The SBNN hasn't received the OP_SET_REPLICATION yet, so it marks the block as under-replicated.
> In the case of raising replication (eg from 1 to 3) we get the opposite problem: the
SBNN marks the block as over-replicated and adds two of the replicas to its invalidation list.
> Generation stamps don't help here, because changing replication level of a block doesn't
change its gen-stamp (and it shouldn't). One possible answer is that we need to modify FSNamesystem.isPopulatingReplQueues
to return false on the standby, and then when it switches from standby to active, initialize
the replication queues only after reading the latest edits... I think that will solve the
SET_REPLICATION issue, but not certain if it will solve all the issues in this general class.

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