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https://issues.apache.org/jira/browse/HDFS-14039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16676755#comment-16676755
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Kitti Nanasi commented on HDFS-14039:
-------------------------------------
Thanks for the comment [~xiaochen]!
I agree that the first one would be the best and we could implement that in a
future trunk for compatibility reasons.
For now we could do something like the #3, but as you said it would not be good
if someone typo-ed the policy name, I suggest to skip the default policy, not
if the default policy is invalid, but if it is empty.
I realised that currently if you explicitly set the default policy to empty (or
to spaces) in the config, then it won't check if the default policy name is
valid or not and won't enable it either. It is because of the code I pasted
below (because of the first if). That is not good, because if you later set a
policy on a folder using the default value, it will give an error with the
message "Policy ' ' does not match any enabled erasure coding policies: []. An
erasure coding policy can be enabled by enableErasureCodingPolicy API."
So I created a patch which gives back a proper error message if default policy
is used when there is none set (empty string is set). And if the empty policy
is set, it is possible to persist all policies in a disabled state.
{code:java}
final String defaultPolicyName = conf.getTrimmed(
DFSConfigKeys.DFS_NAMENODE_EC_SYSTEM_DEFAULT_POLICY,
DFSConfigKeys.DFS_NAMENODE_EC_SYSTEM_DEFAULT_POLICY_DEFAULT);
if (!defaultPolicyName.isEmpty()) {
final ErasureCodingPolicyInfo info =
policiesByName.get(defaultPolicyName);
if (info == null) {
String names = policiesByName.values()
.stream().map((pi) -> pi.getPolicy().getName())
.collect(Collectors.joining(", "));
String msg = String.format("EC policy '%s' specified at %s is not a "
+ "valid policy. Please choose from list of available "
+ "policies: [%s]",
defaultPolicyName,
DFSConfigKeys.DFS_NAMENODE_EC_SYSTEM_DEFAULT_POLICY,
names);
throw new IOException(msg);
}
info.setState(ErasureCodingPolicyState.ENABLED);
enabledPoliciesByName.put(info.getPolicy().getName(), info.getPolicy());
}
{code}
> 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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