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https://issues.apache.org/jira/browse/HDFS-16438?focusedWorklogId=716975&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-716975
]
ASF GitHub Bot logged work on HDFS-16438:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 28/Jan/22 10:32
Start Date: 28/Jan/22 10:32
Worklog Time Spent: 10m
Work Description: tomscut commented on pull request #3928:
URL: https://github.com/apache/hadoop/pull/3928#issuecomment-1024085323
> > ```
> > + if (!isBlockReplicatedOk(dn, b, false, null)) {
> > ```
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > Hi @sodonnel , I just want to make sure that we don't have to take the
inverse here? Please point me out if I understand wrong.
> > ```
> > while(iterator.hasNext()) {
> > + BlockInfo b = iterator.next();
> > + if (isBlockReplicatedOk(dn, b, false, null)) {
> > + iterator.remove();
> > + }
> > + }
> > ```
>
> Yes you are correct, my suggested code has it wrong. We need to remove
from the list if it is replicated OK. The original code only added if it was
not replicated OK.
Thanks @sodonnel for your quick reply. I'll update the code and do some
related tests later.
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Issue Time Tracking
-------------------
Worklog Id: (was: 716975)
Time Spent: 3.5h (was: 3h 20m)
> Avoid holding read locks for a long time when scanDatanodeStorage
> -----------------------------------------------------------------
>
> Key: HDFS-16438
> URL: https://issues.apache.org/jira/browse/HDFS-16438
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: tomscut
> Assignee: tomscut
> Priority: Major
> Labels: pull-request-available
> Attachments: image-2022-01-25-23-18-30-275.png
>
> Time Spent: 3.5h
> Remaining Estimate: 0h
>
> At the time of decommission, if use {*}DatanodeAdminBackoffMonitor{*}, there
> is a heavy operation: {*}scanDatanodeStorage{*}. If the number of blocks on a
> storage is large(more than 5 hundred thousand), and GC performance is also
> poor, it may hold *read lock* for a long time, we should optimize it.
> !image-2022-01-25-23-18-30-275.png|width=764,height=193!
> {code:java}
> 2021-12-22 07:49:01,279 INFO namenode.FSNamesystem
> (FSNamesystemLock.java:readUnlock(220)) - FSNamesystem scanDatanodeStorage
> read lock held for 5491 ms via
> java.lang.Thread.getStackTrace(Thread.java:1552)
> org.apache.hadoop.util.StringUtils.getStackTrace(StringUtils.java:1032)
> org.apache.hadoop.hdfs.server.namenode.FSNamesystemLock.readUnlock(FSNamesystemLock.java:222)
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.readUnlock(FSNamesystem.java:1641)
> org.apache.hadoop.hdfs.server.blockmanagement.DatanodeAdminBackoffMonitor.scanDatanodeStorage(DatanodeAdminBackoffMonitor.java:646)
> org.apache.hadoop.hdfs.server.blockmanagement.DatanodeAdminBackoffMonitor.checkForCompletedNodes(DatanodeAdminBackoffMonitor.java:417)
> org.apache.hadoop.hdfs.server.blockmanagement.DatanodeAdminBackoffMonitor.check(DatanodeAdminBackoffMonitor.java:300)
> org.apache.hadoop.hdfs.server.blockmanagement.DatanodeAdminBackoffMonitor.run(DatanodeAdminBackoffMonitor.java:201)
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
> java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> java.lang.Thread.run(Thread.java:745)
> Number of suppressed read-lock reports: 0
> Longest read-lock held interval: 5491 {code}
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