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From "Sumit Kumar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10400) Incorporate new S3A FileSystem implementation
Date Thu, 05 Jun 2014 21:28:03 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10400?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14019299#comment-14019299
] 

Sumit Kumar commented on HADOOP-10400:
--------------------------------------

Few observations:

# Should it include tests to verify behavior when a user tries to write paths that have multiple
"/" such as s3a://foo////bar/delta///gammma//abc? How is this implementation handling this
would be interesting because each occurance of "/" would appear a directory for current implementation?
# Should it have more logic to consider _$folder$ as marker as well for folders like it's
doing for "/" (by creating fake directories). That way the implementation would be exactly
the same as current s3n. If item #1 fails, i don't see another approach to solve folder representation
in s3.
# aws-java-sdk provides https://github.com/aws/aws-sdk-java/blob/master/src/main/java/com/amazonaws/auth/DefaultAWSCredentialsProviderChain.java
Should we consider adding ProfileCredentialsProvider as described here https://java.awsblog.com/post/TxRE9V31UFN860/Secure-Local-Development-with-the-ProfileCredentialsProvider
This might be a big boon in testing s3 behaviors as unit tests (it's always been really hard
keeping code/xmls checked-into code bases having the access and secret keys). 
# Should S3AFileStatus be more strict in contructor arguments, for example, if it's a directory
constructor do we need isdir flag? Should this be more clearer api?
# Should it be doing parallel rename/delete operations as well? More specifically could copy
operations (while renaming a folder) leverage parallel threads using TransferManager apis?
# Should it implement the iterative listing api as well for better performance and build listStatus
on top of the same?

> Incorporate new S3A FileSystem implementation
> ---------------------------------------------
>
>                 Key: HADOOP-10400
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10400
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs, fs/s3
>    Affects Versions: 2.4.0
>            Reporter: Jordan Mendelson
>            Assignee: Jordan Mendelson
>         Attachments: HADOOP-10400-1.patch, HADOOP-10400-2.patch, HADOOP-10400-3.patch,
HADOOP-10400-4.patch, HADOOP-10400-5.patch
>
>
> The s3native filesystem has a number of limitations (some of which were recently fixed
by HADOOP-9454). This patch adds an s3a filesystem which uses the aws-sdk instead of the jets3t
library. There are a number of improvements over s3native including:
> - Parallel copy (rename) support (dramatically speeds up commits on large files)
> - AWS S3 explorer compatible empty directories files "xyz/" instead of "xyz_$folder$"
(reduces littering)
> - Ignores s3native created _$folder$ files created by s3native and other S3 browsing
utilities
> - Supports multiple output buffer dirs to even out IO when uploading files
> - Supports IAM role-based authentication
> - Allows setting a default canned ACL for uploads (public, private, etc.)
> - Better error recovery handling
> - Should handle input seeks without having to download the whole file (used for splits
a lot)
> This code is a copy of https://github.com/Aloisius/hadoop-s3a with patches to various
pom files to get it to build against trunk. I've been using 0.0.1 in production with CDH 4
for several months and CDH 5 for a few days. The version here is 0.0.2 which changes around
some keys to hopefully bring the key name style more inline with the rest of hadoop 2.x.
> *Tunable parameters:*
>     fs.s3a.access.key - Your AWS access key ID (omit for role authentication)
>     fs.s3a.secret.key - Your AWS secret key (omit for role authentication)
>     fs.s3a.connection.maximum - Controls how many parallel connections HttpClient spawns
(default: 15)
>     fs.s3a.connection.ssl.enabled - Enables or disables SSL connections to S3 (default:
true)
>     fs.s3a.attempts.maximum - How many times we should retry commands on transient errors
(default: 10)
>     fs.s3a.connection.timeout - Socket connect timeout (default: 5000)
>     fs.s3a.paging.maximum - How many keys to request from S3 when doing directory listings
at a time (default: 5000)
>     fs.s3a.multipart.size - How big (in bytes) to split a upload or copy operation up
into (default: 104857600)
>     fs.s3a.multipart.threshold - Until a file is this large (in bytes), use non-parallel
upload (default: 2147483647)
>     fs.s3a.acl.default - Set a canned ACL on newly created/copied objects (private |
public-read | public-read-write | authenticated-read | log-delivery-write | bucket-owner-read
| bucket-owner-full-control)
>     fs.s3a.multipart.purge - True if you want to purge existing multipart uploads that
may not have been completed/aborted correctly (default: false)
>     fs.s3a.multipart.purge.age - Minimum age in seconds of multipart uploads to purge
(default: 86400)
>     fs.s3a.buffer.dir - Comma separated list of directories that will be used to buffer
file writes out of (default: uses ${hadoop.tmp.dir}/s3a )
> *Caveats*:
> Hadoop uses a standard output committer which uploads files as filename.COPYING before
renaming them. This can cause unnecessary performance issues with S3 because it does not have
a rename operation and S3 already verifies uploads against an md5 that the driver sets on
the upload request. While this FileSystem should be significantly faster than the built-in
s3native driver because of parallel copy support, you may want to consider setting a null
output committer on our jobs to further improve performance.
> Because S3 requires the file length and MD5 to be known before a file is uploaded, all
output is buffered out to a temporary file first similar to the s3native driver.
> Due to the lack of native rename() for S3, renaming extremely large files or directories
make take a while. Unfortunately, there is no way to notify hadoop that progress is still
being made for rename operations, so your job may time out unless you increase the task timeout.
> This driver will fully ignore _$folder$ files. This was necessary so that it could interoperate
with repositories that have had the s3native driver used on them, but means that it won't
recognize empty directories that s3native has been used on.
> Statistics for the filesystem may be calculated differently than the s3native filesystem.
When uploading a file, we do not count writing the temporary file on the local filesystem
towards the local filesystem's written bytes count. When renaming files, we do not count the
S3->S3 copy as read or write operations. Unlike the s3native driver, we only count bytes
written when we start the upload (as opposed to the write calls to the temporary local file).
The driver also counts read & write ops, but they are done mostly to keep from timing
out on large s3 operations.
> The AWS SDK unfortunately passes the multipart threshold as an int which means
> fs.s3a.multipart.threshold can not be greater than 2^31-1 (2147483647).
> This is currently implemented as a FileSystem and not a AbstractFileSystem.



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