[jira] [Resolved] (HADOOP-13525) Optimize uses of FS operations in the ASF analysis frameworks and libraries

["Steve Loughran (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-13525?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steve Loughran resolved HADOOP-13525.
-------------------------------------
    Fix Version/s: 3.3.1
       Resolution: Done

we've done some here, leave rest to individual projects

we can/should do the right things in our own code, e.g. distcp

> Optimize uses of FS operations in the ASF analysis frameworks and libraries 
> ----------------------------------------------------------------------------
>
>                 Key: HADOOP-13525
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13525
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs, fs/s3
>    Affects Versions: 2.8.1
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>            Priority: Major
>             Fix For: 3.3.1
>
>
> Review uses of the FS APIs in applications using the Hadoop FS API to access filesystems; identify suboptimal uses and tune them for better performance against HDFS and object stores
> * Assume arbitrary Hadoop 2.x releases: make no changes which are known to make operations on older versions of Hadoop slower
> * Do propose those changes which deliver speedups in later versions of Hadoop, while not impacting older versions, or risk of causing scalability problems.
> * Add more tests, especially scalable ones which also display metrics.
> * Use standard benchmarks and optimization tools to identify hotspots.
> * Use FS behaviour as verified in the FS contract tests as evidence that filesystems correctly implement the Hadoop FS APIs. If a use of an API call is made which hints at the expectation of different/untested behaviours, leave alone and add new tests to the Hadoop FS contract to determine cross-FS semantics.
> * Focus on the startup, split calculation and directory scanning operations: the ones which slow down entire queries.
> * Eliminate use of {{isDirectory()}},  {{getLength()}}, {{exists()}} if a followon operation ({{getStatus()}},{{delete()}}, ... makes the use redundant.
> * Assume that {{FileStatus}} entries are not cached; the cost of creating them is 1 RPC call against HDFS, 1+ HTTPS call against object stores.
> * Locate calls to the listing operations, identify speedups, especially on recursive directory scans.
> * Identify suboptimal seek patterns (backwards as well as forwards) and attempt to reduce/eliminate through reordering and result caching.
> * Try to reuse the results of previous operations (e.g {{FileStatus}} instances) in follow-on calls.
> * Commonly used file formats (e.g ORC) will have transitive benefits.
> * Frameworks to use predicate pushdown where this delivers speedups
> * Document best practises identified and implemented.



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