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Date: Mon, 2 Feb 2015 23:50:35 +0000 (UTC)
From: "Ming Ma (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12771798.1422902603000.235675.1422921035143@Atlassian.JIRA>
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Subject: [jira] [Commented] (HDFS-7725) Incorrect "nodes in service" metrics
 caused all writes to fail
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    [ https://issues.apache.org/jira/browse/HDFS-7725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14302345#comment-14302345 ] 

Ming Ma commented on HDFS-7725:
-------------------------------

Thanks, [~zhz]. Yes, the logic of "don't modify nn stats if the node is dead" can be moved to HeartbeatManager.

For the trunk version, we can wait for HDFS-7411. If HDFS-7411 isn't going to be in branch-2 anytime soon, then we will need some quick fix. Overall, can anyone find any correctness issue with the current patch?

> Incorrect "nodes in service" metrics caused all writes to fail
> --------------------------------------------------------------
>
>                 Key: HDFS-7725
>                 URL: https://issues.apache.org/jira/browse/HDFS-7725
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Ming Ma
>            Assignee: Ming Ma
>         Attachments: HDFS-7725.patch
>
>
> One of our clusters sometimes couldn't allocate blocks from any DNs. BlockPlacementPolicyDefault complains with the following messages for all DNs.
> {noformat}
> the node is too busy (load:x > y)
> {noformat}
> It turns out the {{HeartbeatManager}}'s {{nodesInService}} was computed incorrectly when admins decomm or recomm dead nodes. Here are two scenarios.
> * Decomm dead nodes. It turns out HDFS-7374 has fixed it; not sure if it is intentional. cc / [~zhz], [~andrew.wang], [~atm] Here is the sequence of event without HDFS-7374.
> ** Cluster has one live node. nodesInService == 1
> ** The node becomes dead. nodesInService == 0
> ** Decomm the node. nodesInService == -1
> * However, HDFS-7374 introduces another inconsistency when recomm is involved.
> ** Cluster has one live node. nodesInService == 1
> ** The node becomes dead. nodesInService == 0
> ** Decomm the node. nodesInService == 0
> ** Recomm the node. nodesInService == 1


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