[
https://issues.apache.org/jira/browse/HDFS-16438?focusedWorklogId=716422&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-716422
]
ASF GitHub Bot logged work on HDFS-16438:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 27/Jan/22 14:00
Start Date: 27/Jan/22 14:00
Worklog Time Spent: 10m
Work Description: sodonnel commented on pull request #3928:
URL: https://github.com/apache/hadoop/pull/3928#issuecomment-1023240381
Yea looks likes it is all the isReplicatedOK that is making it slow. What
about a change like this, to move the replicated check outside of the lock:
```
---
a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeAdminBackoffMonitor.java
+++
b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeAdminBackoffMonitor.java
@@ -652,24 +652,27 @@ private void scanDatanodeStorage(DatanodeDescriptor dn,
Iterator<BlockInfo> it = s.getBlockIterator();
while (it.hasNext()) {
BlockInfo b = it.next();
- if (!initialScan || dn.isEnteringMaintenance()) {
- // this is a rescan, so most blocks should be replicated now,
- // or this node is going into maintenance. On a healthy
- // cluster using racks or upgrade domain, a node should be
- // able to go into maintenance without replicating many blocks
- // so we will check them immediately.
- if (!isBlockReplicatedOk(dn, b, false, null)) {
- blockList.put(b, null);
- }
- } else {
- blockList.put(b, null);
- }
+ blockList.put(b, null);
numBlocksChecked++;
}
} finally {
namesystem.readUnlock();
}
}
+ if (!initialScan || dn.isEnteringMaintenance()) {
+ // this is a rescan, so most blocks should be replicated now,
+ // or this node is going into maintenance. On a healthy
+ // cluster using racks or upgrade domain, a node should be
+ // able to go into maintenance without replicating many blocks
+ // so we will check them immediately.
+ Iterator<BlockInfo> iterator = blockList.keySet().iterator();
+ while(iterator.hasNext()) {
+ BlockInfo b = iterator.next();
+ if (!isBlockReplicatedOk(dn, b, false, null)) {
+ iterator.remove();
+ }
+ }
+ }
}
```
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Issue Time Tracking
-------------------
Worklog Id: (was: 716422)
Time Spent: 2h (was: 1h 50m)
> 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: 2h
> 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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