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https://issues.apache.org/jira/browse/HDFS-14039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16675884#comment-16675884
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Xiao Chen commented on HDFS-14039:
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Thanks Kitti for revving and an offline discussion.
I don't think disabling the default should fail. Anyone can setPolicy on the
path that they have write permission, but enablePolicy is a superuser op. If an
admin wants to make sure no one in the cluster turns on EC, then disablePolicy
seems to be the only hard guarantee.
Thanks for pointing out my overlook on the default policy behavior offline
though. You're right, if the default is not configured, RS-6-3 is used; if it's
configured, it has to be a valid policy. Combining these 2 facts means that an
admin cannot actually disable EC that persists a restart.
Some options I can think of:
# add a new ECP state 'uninitialized', so we can distinguish between an
explicit disable and the default. This would be the cleanest if it were the
initial implementation, but it would a headache for compatibility
# add another config option to override the default, "do not default to default
if I'm set" kind of config. This works but is rather ugly IMO
# allow admin to configure default to an 'invalid' policy. e.g. if parsing the
{{defaultPolicyName}} yields no ec policy, log a warning instead of throwing an
IOE. This would be a PITA if someone really explicitly configured this but
typo'ed, but that feels like a rather smaller group than the general
I-don't-want-my-users-to-setpolicy group.
Since this is targeted for a maintenance release, how about we do #3 here, and
leave #1 for a future trunk version? Any other ideas?
> ec -listPolicies doesn't show correct state for the default policy when the
> default is not RS(6,3)
> --------------------------------------------------------------------------------------------------
>
> Key: HDFS-14039
> URL: https://issues.apache.org/jira/browse/HDFS-14039
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: erasure-coding
> Affects Versions: 3.0.0
> Reporter: Xiao Chen
> Assignee: Kitti Nanasi
> Priority: Major
> Attachments: HDFS-14039.001.patch, HDFS-14039.002.patch
>
>
> {noformat}
> $ 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=ENABLED
> 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 ec -enablePolicy -policy XOR-2-1-1024k
> Erasure coding policy XOR-2-1-1024k is enabled
> $ 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=ENABLED
> 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=ENABLED
> ----------------------------------
> $ #set default to be RS-3-2 for dfs.namenode.ec.system.default.policy, and
> restart NN
> (this seems to be what's triggering the failure)
> -----------------------------------
> $ 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=ENABLED
> 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=ENABLED
> $ hdfs ec -enablePolicy -policy RS-3-2-1024k
> Erasure coding policy RS-3-2-1024k is enabled
> $ 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=ENABLED
> 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=ENABLED
> {noformat}
> The last 2 should show RS-3-2 as ENABLED. RS-6-3 DISABLED if it's not enabled
> before.
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