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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