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https://issues.apache.org/jira/browse/HDFS-16521?focusedWorklogId=763037&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-763037
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ASF GitHub Bot logged work on HDFS-16521:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 27/Apr/22 16:40
Start Date: 27/Apr/22 16:40
Worklog Time Spent: 10m
Work Description: saintstack commented on code in PR #4107:
URL: https://github.com/apache/hadoop/pull/4107#discussion_r860008767
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hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSCommands.md:
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@@ -394,7 +394,7 @@ Usage:
| COMMAND\_OPTION | Description |
|:--
Issue Time Tracking
-------------------
Worklog Id: (was: 763037)
Time Spent: 4h 20m (was: 4h 10m)
> DFS API to retrieve slow datanodes
> ----------------------------------
>
> Key: HDFS-16521
> URL: https://issues.apache.org/jira/browse/HDFS-16521
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Viraj Jasani
> Assignee: Viraj Jasani
> Priority: Major
> Labels: pull-request-available
> Time Spent: 4h 20m
> Remaining Estimate: 0h
>
> Providing DFS API to retrieve slow nodes would help add an additional option
> to "dfsadmin -report" that lists slow datanodes info for operators to take a
> look, specifically useful filter for larger clusters.
> The other purpose of such API is for HDFS downstreamers without direct access
> to namenode http port (only rpc port accessible) to retrieve slownodes.
> Moreover,
> [FanOutOneBlockAsyncDFSOutput|https://github.com/apache/hbase/blob/master/hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/FanOutOneBlockAsyncDFSOutput.java]
> in HBase currently has to rely on it's own way of marking and excluding slow
> nodes while 1) creating pipelines and 2) handling ack, based on factors like
> the data length of the packet, processing time with last ack timestamp,
> whether flush to replicas is finished etc. If it can utilize slownode API
> from HDFS to exclude nodes appropriately while writing block, a lot of it's
> own post-ack computation of slow nodes can be _saved_ or _improved_ or based
> on further experiment, we could find _better solution_ to manage slow node
> detection logic both in HDFS and HBase. However, in order to collect more
> data points and run more POC around this area, HDFS should provide API for
> downstreamers to efficiently utilize slownode info for such critical
> low-latency use-case (like writing WALs).
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