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https://issues.apache.org/jira/browse/HDFS-11047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16059210#comment-16059210
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Brahma Reddy Battula commented on HDFS-11047:
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IMHO, this will be good candidate to go branch-2.7. [~xiaobingo] can you update
the branch-2.7 patch also..?
> Remove deep copies of FinalizedReplica to alleviate heap consumption on
> DataNode
> --------------------------------------------------------------------------------
>
> Key: HDFS-11047
> URL: https://issues.apache.org/jira/browse/HDFS-11047
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Xiaobing Zhou
> Assignee: Xiaobing Zhou
> Fix For: 2.8.0, 3.0.0-alpha2
>
> Attachments: HDFS-11047.000.patch, HDFS-11047.001.patch,
> HDFS-11047.002.patch, HDFS-11047-branch-2.002.patch
>
>
> DirectoryScanner does scan by deep copying FinalizedReplica. In a deployment
> with 500,000+ blocks, we've seen the DN heap usage being accumulated to high
> peaks very quickly. Deep copies of FinalizedReplica will make DN heap usage
> even worse if directory scans are scheduled more frequently. This proposes
> removing unnecessary deep copies since DirectoryScanner#scan already holds
> lock of dataset.
> DirectoryScanner#scan
> {code}
> try(AutoCloseableLock lock = dataset.acquireDatasetLock()) {
> for (Entry<String, ScanInfo[]> entry : diskReport.entrySet()) {
> String bpid = entry.getKey();
> ScanInfo[] blockpoolReport = entry.getValue();
>
> Stats statsRecord = new Stats(bpid);
> stats.put(bpid, statsRecord);
> LinkedList<ScanInfo> diffRecord = new LinkedList<ScanInfo>();
> diffs.put(bpid, diffRecord);
>
> statsRecord.totalBlocks = blockpoolReport.length;
> List<ReplicaInfo> bl = dataset.getFinalizedBlocks(bpid); /* deep
> copies here*/
> {code}
> FsDatasetImpl#getFinalizedBlocks
> {code}
> public List<ReplicaInfo> getFinalizedBlocks(String bpid) {
> try (AutoCloseableLock lock = datasetLock.acquire()) {
> ArrayList<ReplicaInfo> finalized =
> new ArrayList<ReplicaInfo>(volumeMap.size(bpid));
> for (ReplicaInfo b : volumeMap.replicas(bpid)) {
> if (b.getState() == ReplicaState.FINALIZED) {
> finalized.add(new ReplicaBuilder(ReplicaState.FINALIZED)
> .from(b).build()); /* deep copies here*/
> }
> }
> return finalized;
> }
> }
> {code}
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