Steve Loughran created HADOOP-13525:
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Summary: Optimize uses of FS operations in the ASF analysis
frameworks,
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: 2.7.2
Reporter: Steve Loughran
Assignee: Steve Loughran
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.
* Document best practises identified and implemented.
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