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https://issues.apache.org/jira/browse/HDFS-12682?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiao Chen updated HDFS-12682:
-----------------------------
Attachment: HDFS-12682.04.patch
Attaching patch 4 which is a hybrid solution between the approaches in patch 2
and patch 3.
To summarize the concerns, they're mostly:
# ECP should be immutable
# Compatibility
# Code easy to maintain / read
In patch 4, protobuf is untouched, and the Java class {{ErasureCodingPolicy}}
is modified to represent the immutable version of a policy. A new Java class
{{ErasureCodingPoilcyInfo}} is added, containing the ECP and its state.
When serializing and deserializing the protobuf, we conditionally convert it to
a ECP or ECPI, based on necessity. The ECPs are still cached by
{{SystemErasureCodingPolicies}} regardlessly.
There is a slight incompatibility of {{LimitedPrivate}}
{{DistributedFileSystem}} and {{Public}} {{Evolving}} {{HdfsAdmin}}, but this
feels to be best solution to me.
Also addressed Eddy's comment about making the ECP classes private, and
Rakesh's comment about removing the setters of id/name from ECP.
Regarding Kai's comment of {{we should unify all the EC policies}}, I think we
can do a separate jira to basically change {{SystemErasureCodingPolicies}} to
be {{ErasureCodingPoliciesCache}} or the like. IIUC this can be a separate
improvement jira.
Thanks all for the reviews!
> ECAdmin -listPolicies will always show SystemErasureCodingPolicies state as
> DISABLED
> ------------------------------------------------------------------------------------
>
> Key: HDFS-12682
> URL: https://issues.apache.org/jira/browse/HDFS-12682
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: erasure-coding
> Reporter: Xiao Chen
> Assignee: Xiao Chen
> Priority: Blocker
> Labels: hdfs-ec-3.0-must-do
> Attachments: HDFS-12682.01.patch, HDFS-12682.02.patch,
> HDFS-12682.03.patch, HDFS-12682.04.patch
>
>
> On a real cluster, {{hdfs ec -listPolicies}} will always show policy state as
> DISABLED.
> {noformat}
> [hdfs@nightly6x-1 root]$ hdfs ec -listPolicies
> Erasure Coding Policies:
> ErasureCodingPolicy=[Name=RS-10-4-1024k, Schema=[ECSchema=[Codec=rs,
> numDataUnits=10, numParityUnits=4]], CellSize=1048576, Id=5, State=DISABLED]
> ErasureCodingPolicy=[Name=RS-3-2-1024k, Schema=[ECSchema=[Codec=rs,
> numDataUnits=3, numParityUnits=2]], CellSize=1048576, Id=2, State=DISABLED]
> ErasureCodingPolicy=[Name=RS-6-3-1024k, Schema=[ECSchema=[Codec=rs,
> numDataUnits=6, numParityUnits=3]], CellSize=1048576, Id=1, State=DISABLED]
> ErasureCodingPolicy=[Name=RS-LEGACY-6-3-1024k,
> Schema=[ECSchema=[Codec=rs-legacy, numDataUnits=6, numParityUnits=3]],
> CellSize=1048576, Id=3, State=DISABLED]
> ErasureCodingPolicy=[Name=XOR-2-1-1024k, Schema=[ECSchema=[Codec=xor,
> numDataUnits=2, numParityUnits=1]], CellSize=1048576, Id=4, State=DISABLED]
> [hdfs@nightly6x-1 root]$ hdfs ec -getPolicy -path /ecec
> XOR-2-1-1024k
> {noformat}
> This is because when [deserializing
> protobuf|https://github.com/apache/hadoop/blob/branch-3.0.0-beta1/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocolPB/PBHelperClient.java#L2942],
> the static instance of [SystemErasureCodingPolicies
> class|https://github.com/apache/hadoop/blob/branch-3.0.0-beta1/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/SystemErasureCodingPolicies.java#L101]
> is first checked, and always returns the cached policy objects, which are
> created by default with state=DISABLED.
> All the existing unit tests pass, because that static instance that the
> client (e.g. ECAdmin) reads in unit test is updated by NN. :)
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