[jira] [Commented] (HDFS-7725) Incorrect "nodes in service" metrics caused all writes to fail

["Zhe Zhang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-7725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14387675#comment-14387675 ] 

Zhe Zhang commented on HDFS-7725:
---------------------------------

Thanks Ming. The patch looks good to me. It basically bypasses {{HeartbeatManager}} in stop decomm since start decomm is already bypassing it.

> 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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