[jira] [Created] (HDFS-12136) BlockSender performance regression due to volume scanner edge case

["Daryn Sharp (JIRA)" <ji...@apache.org>]

Daryn Sharp created HDFS-12136:
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             Summary: BlockSender performance regression due to volume scanner edge case
                 Key: HDFS-12136
                 URL: https://issues.apache.org/jira/browse/HDFS-12136
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: datanode
    Affects Versions: 2.8.0
            Reporter: Daryn Sharp
            Assignee: Daryn Sharp
            Priority: Critical


HDFS-11160 attempted to fix a volume scan race for a file appended mid-scan by reading the last checksum of finalized blocks within the {{BlockSender}} ctor.  Unfortunately it's holding the exclusive dataset lock to open and read the metafile multiple times  Block sender instantiation becomes serialized.

Performance completely collapses under heavy disk i/o utilization or high xceiver activity.  Ex. lost node replication, balancing, or decommissioning.  The xceiver threads congest creating block senders and impair the heartbeat processing that is contending for the same lock.  Combined with other lock contention issues, pipelines break and nodes sporadically go dead.



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