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https://issues.apache.org/jira/browse/HDFS-7337?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14632005#comment-14632005
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Andrew Wang commented on HDFS-7337:
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Hi [~drankye], this JIRA resurfaced due to discussion on HDFS-8059 and also the
need to persist this information in the fsimage/editlog, I was hoping we could
clarify the configuration language for an EC codec and schema.
I read through the v3 design doc, and please let me know if you think the
following would work:
Schema (stored on EC zone or INode as a PB so we can evolve it):
* Codec enum (e.g. RS, LRC, etc), which would also have a friendly
human-readable name. The enum is good for efficiency and so the user can only
pick from supported codecs.
* List of k,v pairs for configuration. This could be used for k, m, and any
other arbitrary parameters needed by the codec. Very general.
Client-side:
* Client would validate the codec of a file against the codecs supported in its
own software version. This way, if we add a new codec type, we can restrict old
clients from reading it.
* In client's hdfs-site.xml, we can configure a codec implementation for every
codec. This would look something like e.g.
{{dfs.client.ec.codec.reed-solomon.impl = org.apache.hadoop....isal}}, saying
to use ISA-L for reed-solomon.
This is just to get us going for phase 1. We'd be restricting users to choosing
from a list of known-good codecs, while they could still provide their own
codec implementations as long as they implement the interfaces.
When we get to the point of fully-pluggable codecs, we can add a special
"wildcard" enum value to support this, and then potentially add new fields to
the PB if required. This will require another HDFS upgrade before we can
support full pluggability, but it sounds like we still need to figure out
interfaces for things like block placement and recovery logic anyway.
> 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-v3.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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