hadoop-hdfs-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "David Mollitor (Jira)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13157) Do Not Remove Blocks Sequentially During Decommission
Date Thu, 29 Aug 2019 21:55:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16918978#comment-16918978

David Mollitor commented on HDFS-13157:

Yup.  That's how I plan on improving this:

    private void update() {
      while(index < iterators.size() - 1 && !iterators.get(index).hasNext()) {


I'm going to round-robin this iterator.  Each call to {{next()}} on this {{BlockIterator()}}
will call {{next()}} cyclically on the list of available {{Iterator}}s until they are all
exhausted instead of draining each {{Iterator}} in order.
I just need to see what else might be using this Iterator and see if the other places need
this linear behavior.

> Do Not Remove Blocks Sequentially During Decommission 
> ------------------------------------------------------
>                 Key: HDFS-13157
>                 URL: https://issues.apache.org/jira/browse/HDFS-13157
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode, namenode
>    Affects Versions: 3.0.0
>            Reporter: David Mollitor
>            Assignee: David Mollitor
>            Priority: Major
> From what I understand of [DataNode decommissioning|https://github.com/apache/hadoop/blob/42a1c98597e6dba2e371510a6b2b6b1fb94e4090/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeAdminManager.java] it
appears that all the blocks are scheduled for removal _in order._. I'm not 100% sure what
the ordering is exactly, but I think it loops through each data volume and schedules each
block to be replicated elsewhere. The net affect is that during a decommission, all of the
DataNode transfer threads slam on a single volume until it is cleaned out. At which point,
they all slam on the next volume, etc.
> Please randomize the block list so that there is a more even distribution across all
volumes when decommissioning a node.

This message was sent by Atlassian Jira

To unsubscribe, e-mail: hdfs-issues-unsubscribe@hadoop.apache.org
For additional commands, e-mail: hdfs-issues-help@hadoop.apache.org

View raw message