[jira] [Resolved] (HDFS-5664) try to relieve the BlockReaderLocal read() synchronized hotspot

["Andrew Kyle Purtell (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-5664?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andrew Kyle Purtell resolved HDFS-5664.
---------------------------------------
      Assignee:     (was: Liang Xie)
    Resolution: Incomplete

> try to relieve the BlockReaderLocal read() synchronized hotspot
> ---------------------------------------------------------------
>
>                 Key: HDFS-5664
>                 URL: https://issues.apache.org/jira/browse/HDFS-5664
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 2.2.0, 3.0.0-alpha1
>            Reporter: Liang Xie
>            Priority: Major
>
> Current the BlockReaderLocal's read has a synchronized modifier:
> {code}
> public synchronized int read(byte[] buf, int off, int len) throws IOException {
> {code}
> In a HBase physical read heavy cluster, we observed some hotspots from dfsclient path, the detail strace trace could be found from: https://issues.apache.org/jira/browse/HDFS-1605?focusedCommentId=13843241&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13843241
> I haven't looked into the detail yet, put some raw ideas here firstly:
> 1) replace synchronized with try lock with timeout pattern, so could fail-fast,  2) fallback to non-ssr mode if get a local reader lock failed.
> There're two suitable scenario at least to remove this hotspot:
> 1) Local physical read heavy, e.g. HBase block cache miss ratio is high
> 2) slow/bad disk.
> It would be helpful to achive a lower 99th percentile HBase read latency somehow.



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