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https://issues.apache.org/jira/browse/HADOOP-13208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15402954#comment-15402954
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Chris Nauroth commented on HADOOP-13208:
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{quote}
What is this for? I see it was introduced in HADOOP-13131, but don't see
any usage of the configuration flag it sets (fs.s3a.impl.disable.cache).
{quote}
[~fabbri], sorry, I missed this comment last time around.
This logic disables the {{FileSystem}} cache. The logic for this is inside the
{{FileSystem}} base class. (See the static {{FileSystem#get(URI,
Configuration)}} method.) Whether or not the cache is in effect is determined
by a dynamic configuration property: {{fs.<scheme>.impl.disable.cache}}.
In some cases, we might have a test suite with multiple test methods that all
want to test slightly different configuration. However, all tests in a suite
execute in the same process, so there would be a risk of reusing a cached
instance across multiple tests. Unfortunately, the caching is not sensitive to
changes in the {{Configuration}} instance. (The cache key is the scheme,
authority, and {{UserGroupInformation}}.) To work around that, we disable the
cache for these tests.
> S3A listFiles(recursive=true) to do a bulk listObjects instead of walking the
> pseudo-tree of directories
> --------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-13208
> URL: https://issues.apache.org/jira/browse/HADOOP-13208
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 2.8.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Minor
> Attachments: HADOOP-13208-branch-2-001.patch,
> HADOOP-13208-branch-2-007.patch, HADOOP-13208-branch-2-008.patch,
> HADOOP-13208-branch-2-009.patch, HADOOP-13208-branch-2-010.patch,
> HADOOP-13208-branch-2-011.patch, HADOOP-13208-branch-2-012.patch,
> HADOOP-13208-branch-2-017.patch, HADOOP-13208-branch-2-018.patch
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> A major cost in split calculation against object stores turns out be listing
> the directory tree itself. That's because against S3, it takes S3A two HEADs
> and two lists to list the content of any directory path (2 HEADs + 1 list for
> getFileStatus(); the next list to query the contents).
> Listing a directory could be improved slightly by combining the final two
> listings. However, a listing of a directory tree will still be
> O(directories). In contrast, a recursive {{listFiles()}} operation should be
> implementable by a bulk listing of all descendant paths; one List operation
> per thousand descendants.
> As the result of this call is an iterator, the ongoing listing can be
> implemented within the iterator itself
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