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https://issues.apache.org/jira/browse/HDFS-7337?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14359825#comment-14359825
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Kai Zheng commented on HDFS-7337:
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Thanks [~zhz] for the review and thoughts.
bq.ErasureCodec is like a factory or an utility class, which creates
ErasureCoder and BlockGrouper based on ECSchema
{{ErasureCodec}} would be the high level construct in the framework that covers
all the potential erasure code specific aspects, including but might not be
limited to {{ErasureCoder}} and {{BlockGrouper}}, which allows to be
implemented and deployed as a whole for a new code. All the underlying code
specific logic can be hooked via codec and can only be accessible thru codec. I
understand there will be something more to think about, it's generally one of
the major goal for the framework.
bq.I think we can leverage the pattern of BlockStoragePolicySuite
It's a good pattern. {{ErasureCodec}} follows another good pattern,
{{CompressionCodec}}.
bq. Something like:...your illustration codes...
I understand we need to hard-code a default schema for the system. What we have
discussed and been doing is we allow to predefine EC schemas in an external
file (XML currently used as we regularly do in the project). For easy
reference, unique schema name (string) and codec name (string) are used. Do you
have any concern for this way ?
bq.Then NN can just pass around the schema ID when communicating with DN and
client, which is much smaller than an ErasureCodec object.
Yes similarly it's to pass around the schema NAME between any pair among NN,
DN, client. It's not meaning to pass ErasureCodec object. Is there confusing
sentence I need to clarify in the doc ? All the {{ErasureCodec}}s are loaded
thru core-site configuration or service locators, and kept in map with codec
name as the key. Providing the codec name, a codec will be fetched from the
map. Codec object isn't needed to be passed around, codec name is. I guess
you're meaning schema object. In the f2f meetup discussion with [~jingzhao], we
mentioned it may need to pass around schema object. If we don't want to
hard-code all the schemas, then we need to pass schema object I guess.
> Configurable and pluggable Erasure Codec and schema
> ---------------------------------------------------
>
> Key: HDFS-7337
> URL: https://issues.apache.org/jira/browse/HDFS-7337
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Zhe Zhang
> Assignee: Kai Zheng
> Attachments: HDFS-7337-prototype-v1.patch,
> HDFS-7337-prototype-v2.zip, HDFS-7337-prototype-v3.zip,
> PluggableErasureCodec-v2.pdf, PluggableErasureCodec.pdf
>
>
> According to HDFS-7285 and the design, this considers to support multiple
> Erasure Codecs via pluggable approach. It allows to define and configure
> multiple codec schemas with different coding algorithms and parameters. The
> resultant codec schemas can be utilized and specified via command tool for
> different file folders. While design and implement such pluggable framework,
> it’s also to implement a concrete codec by default (Reed Solomon) to prove
> the framework is useful and workable. Separate JIRA could be opened for the
> RS codec implementation.
> Note HDFS-7353 will focus on the very low level codec API and implementation
> to make concrete vendor libraries transparent to the upper layer. This JIRA
> focuses on high level stuffs that interact with configuration, schema and etc.
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