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https://issues.apache.org/jira/browse/HDFS-15406?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17136797#comment-17136797
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Stephen O'Donnell commented on HDFS-15406:
------------------------------------------
Going from 3m20 to 52 seconds with such a simple change is a big win.
It would be great to see how long the sort call takes on this line:
{code}
Collections.sort(bl); // Sort based on blockId
{code}
My feeling is that we can just drop this call due to the already sorted
FoldedTreeSet, but it might be best to create a new method on FSDatasetSPI
called getSortedFinalizedBlocks to make it obvious, as there are possibly other
implementations of FSDatasetImpl which may not have the blocks already sorted.
If you don't want to investigate that as part of this Jira, we can create a
sub-jira for it. It might be a trivial change to improve things a bit further,
perhaps saving about another 5 seconds.
> Improve the speed of Datanode Block Scan
> ----------------------------------------
>
> Key: HDFS-15406
> URL: https://issues.apache.org/jira/browse/HDFS-15406
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: hemanthboyina
> Assignee: hemanthboyina
> Priority: Major
> Attachments: HDFS-15406.001.patch
>
>
> In our customer cluster we have approx 10M blocks in one datanode
> the Datanode to scans all the blocks , it has taken nearly 5mins
> {code:java}
> 2020-06-10 12:17:06,869 | INFO |
> java.util.concurrent.ThreadPoolExecutor$Worker@3b4bea70[State = -1, empty
> queue] | BlockPool BP-1104115233-**.**.**.**-1571300215588 Total blocks:
> 11149530, missing metadata files:472, missing block files:472, missing blocks
> in memory:0, mismatched blocks:0 | DirectoryScanner.java:473
> 2020-06-10 12:17:06,869 | WARN |
> java.util.concurrent.ThreadPoolExecutor$Worker@3b4bea70[State = -1, empty
> queue] | Lock held time above threshold: lock identifier:
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl
> lockHeldTimeMs=329854 ms. Suppressed 0 lock warnings. The stack trace is:
> java.lang.Thread.getStackTrace(Thread.java:1559)
> org.apache.hadoop.util.StringUtils.getStackTrace(StringUtils.java:1032)
> org.apache.hadoop.util.InstrumentedLock.logWarning(InstrumentedLock.java:148)
> org.apache.hadoop.util.InstrumentedLock.check(InstrumentedLock.java:186)
> org.apache.hadoop.util.InstrumentedLock.unlock(InstrumentedLock.java:133)
> org.apache.hadoop.util.AutoCloseableLock.release(AutoCloseableLock.java:84)
> org.apache.hadoop.util.AutoCloseableLock.close(AutoCloseableLock.java:96)
> org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.scan(DirectoryScanner.java:475)
> org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.reconcile(DirectoryScanner.java:375)
> org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.run(DirectoryScanner.java:320)
> 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:1149)
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> java.lang.Thread.run(Thread.java:748)
> | InstrumentedLock.java:143 {code}
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