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https://issues.apache.org/jira/browse/HDFS-15715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17248729#comment-17248729
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zhengchenyu edited comment on HDFS-15715 at 12/14/20, 3:52 AM:
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I solve this problem, and run on one cluster in near one week. But our version
is hadoop-2.7.3. Because after hadoop-2.8, moudle hadoop-hdfs was split with
multi maven moudle. So I submited a ugly patch, this is not final version. I
only wanna show how to slove this problem. I submited HDFS-15715.001.patch.
I think there will be two way to solve this problem：
(1) recode chooseStorageTypes, and remove the result which is not meet storage
policy demand from results.
(2) remove the result which is not meet storage policy demand from results,
after chooseStorageTypes.
I choose first way, becuase I thinks it save calculation. To label it, i use a
new method 'chooseStorageTypesWIth Node'. But a little ugly, maybe we need to
reorganize the code.
was (Author: zhengchenyu):
I solve this problem, and run on one cluster in near one week. But our version
is hadoop-2.7.3. Because after hadoop-2.8, moudle hadoop-hdfs was split with
multi maven moudle. So I submited a ugly patch, this is not final version. I
only wanna show how to slove this problem. I submited HDFS-15715.001.patch.
I think there will be two way to solve this problem：
(1) recode chooseStorageTypes, and remove the result which is not meet storage
policy demand from results.
(2) remove the result which is not meet storage policy demand from results,
after chooseStorageTypes.
I choose first way, becuase I thinks it save calculation. But a little ugly,
maybe we need to reorganize the code.
> ReplicatorMonitor performance degrades, when the storagePolicy of many file
> are not match with their real datanodestorage
> --------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-15715
> URL: https://issues.apache.org/jira/browse/HDFS-15715
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 2.7.3, 3.2.1
> Reporter: zhengchenyu
> Assignee: zhengchenyu
> Priority: Major
> Fix For: 3.3.1
>
> Attachments: HDFS-15715.001.patch
>
>
> One of our Namenode which has 300M files and blocks. In common way, this
> namode shoud not be in heavy load. But we found rpc process time keep high,
> and decommission is very slow.
>
> I search the metrics, I found uderreplicated blocks keep high. Then I jstack
> namenode, found 'InnerNode.getLoc' is hot spot cod. I think maybe
> chooseTarget can't find block, so result to performance degradation. Consider
> with HDFS-10453, I guess maybe some logical trigger to the scene where
> chooseTarget can't find proper block.
> Then I enable some debug. (Of course I revise some code so that only debug
> isGoodTarget, because enable BlockPlacementPolicy's debug log is dangrouse).
> I found "the rack has too many chosen nodes" is called. Then I found some log
> like this
> {code}
> 2020-12-04 12:13:56,345 WARN
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to
> place enough replicas, still in need of 0 to reach 3 (unavailableStorages=[],
> storagePolicy=BlockStoragePolicy{HOT:7, storageTypes=[DISK],
> creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, newBlock=false) For
> more information, please enable DEBUG log level on
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy
> 2020-12-04 12:14:03,843 WARN
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to
> place enough replicas, still in need of 0 to reach 3 (unavailableStorages=[],
> storagePolicy=BlockStoragePolicy{COLD:2, storageTypes=[ARCHIVE],
> creationFallbacks=[], replicationFallbacks=[]}, newBlock=false) For more
> information, please enable DEBUG log level on
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy
> {code}
> Then through some debug and simulation, I found the reason, and reproduction
> this exception.
> The reason is that some developer use COLD storage policy and mover, but the
> operatiosn of setting storage policy and mover are asynchronous. So some
> file's real datanodestorages are not match with this storagePolicy.
> Let me simualte this proccess. If /tmp/a is create, then have 2 replications
> are DISK. Then set storage policy to COLD. When some logical trigger(For
> example decommission) to copy this block. chooseTarget then use
> chooseStorageTypes to filter real needed block. Here the size of variable
> requiredStorageTypes which chooseStorageTypes returned is 3. But the size of
> result is 2. But 3 means need 3 ARCHIVE storage. 2 means bocks has 2 DISK
> storage. Then will request to choose 3 target. choose first target is right,
> but when choose seconde target, the variable 'counter' is 4 which is larger
> than maxTargetPerRack which is 3 in function isGoodTarget. So skip all
> datanodestorage. Then result to bad performance.
> I think chooseStorageTypes need to consider the result, when the exist
> replication doesn't meet storage policy's demand, we need to remove this from
> result.
> I changed by this way, and test in my unit-test. Then solve it.
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