Lisheng Sun updated HDFS-14283:
    Attachment: HDFS-14283.001.patch

> DFSInputStream to prefer cached replica
> ---------------------------------------
>                 Key: HDFS-14283
>                 URL: https://issues.apache.org/jira/browse/HDFS-14283
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 2.6.0
>         Environment: HDFS Caching
>            Reporter: Wei-Chiu Chuang
>            Assignee: Lisheng Sun
>            Priority: Major
>         Attachments: HDFS-14283.001.patch
> HDFS Caching offers performance benefits. However, currently NameNode does 
> not treat cached replica with higher priority, so HDFS caching is only useful 
> when cache replication = 3, that is to say, all replicas are cached in 
> memory, so that a client doesn't randomly pick an uncached replica.
> HDFS-6846 proposed to let NameNode give higher priority to cached replica. 
> Changing a logic in NameNode is always tricky so that didn't get much 
> traction. Here I propose a different approach: let client (DFSInputStream) 
> prefer cached replica.
> A {{LocatedBlock}} object already contains cached replica location so a 
> client has the needed information. I think we can change 
> {{DFSInputStream#getBestNodeDNAddrPair()}} for this purpose.

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