[
https://issues.apache.org/jira/browse/HDFS-16420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17494365#comment-17494365
]
Takanobu Asanuma commented on HDFS-16420:
-----------------------------------------
Hi, [~joepep]. I think you mean
BlockPlacementPolicyRackFaultTolerant#pickupReplicaSet, right?
The replica location in exactlyOne doesn't mean that the replica is only one.
It means it is only one identical replica in the same rack. It can be the
candidate for deletion.
Let's think about an EC block group that is RS-6-3 and has excess EC blocks.
|blk_0|blk_1|blk_2|blk_3|blk_4|blk_5|blk_6|blk_7|blk_8|blk_3|
|dn0|dn1|dn2|dn3|dn4|dn5|dn6|dn7|dn8|dn9|
|rack0|rack1|rack2|rack3|rack4|rack5|rack6|rack7|rack8|rack9|
In this case, morethanOne is 0 as every EC block is on a different rack,
exactlyOne is [dn3, dn9] as they have the same excess block, and
pickupReplicaSet should return the exactlyOne.
> Avoid deleting unique data blocks when deleting redundancy striped blocks
> -------------------------------------------------------------------------
>
> Key: HDFS-16420
> URL: https://issues.apache.org/jira/browse/HDFS-16420
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: ec, erasure-coding
> Reporter: qinyuren
> Assignee: Jackson Wang
> Priority: Critical
> Labels: pull-request-available
> Fix For: 3.4.0, 3.2.3, 3.3.2
>
> Attachments: image-2022-01-10-17-31-35-910.png,
> image-2022-01-10-17-32-56-981.png
>
> Time Spent: 2h 10m
> Remaining Estimate: 0h
>
> We have a similar problem as HDFS-16297 described.
> In our cluster, we used {color:#de350b}ec(6+3) + balancer with version
> 3.1.0{color}, and the {color:#de350b}missing block{color} happened.
> We got the block(blk_-9223372036824119008) info from fsck, only 5 live
> replications and multiple redundant replications.
> {code:java}
> blk_-9223372036824119008_220037616 len=133370338 MISSING! Live_repl=5
> blk_-9223372036824119007:DatanodeInfoWithStorage,
> blk_-9223372036824119002:DatanodeInfoWithStorage,
> blk_-9223372036824119001:DatanodeInfoWithStorage,
> blk_-9223372036824119000:DatanodeInfoWithStorage,
> blk_-9223372036824119004:DatanodeInfoWithStorage,
> blk_-9223372036824119004:DatanodeInfoWithStorage,
> blk_-9223372036824119004:DatanodeInfoWithStorage,
> blk_-9223372036824119004:DatanodeInfoWithStorage,
> blk_-9223372036824119004:DatanodeInfoWithStorage,
> blk_-9223372036824119004:DatanodeInfoWithStorage {code}
>
> We searched the log from all datanode, and found that the internal blocks of
> blk_-9223372036824119008 were deleted almost at the same time.
>
> {code:java}
> 08:15:58,550 INFO impl.FsDatasetAsyncDiskService
> (FsDatasetAsyncDiskService.java:run(333)) - Deleted
> BP-1606066499-xxxx-1606188026755 blk_-9223372036824119008_220037616 URI
> file:/data15/hadoop/hdfs/data/current/BP-1606066499-xxxx-1606188026755/current/finalized/subdir19/subdir9/blk_-9223372036824119008
> 08:16:21,214 INFO impl.FsDatasetAsyncDiskService
> (FsDatasetAsyncDiskService.java:run(333)) - Deleted
> BP-1606066499-xxxx-1606188026755 blk_-9223372036824119006_220037616 URI
> file:/data4/hadoop/hdfs/data/current/BP-1606066499-xxxx-1606188026755/current/finalized/subdir19/subdir9/blk_-9223372036824119006
> 08:16:55,737 INFO impl.FsDatasetAsyncDiskService
> (FsDatasetAsyncDiskService.java:run(333)) - Deleted
> BP-1606066499-xxxx-1606188026755 blk_-9223372036824119005_220037616 URI
> file:/data2/hadoop/hdfs/data/current/BP-1606066499-xxxx-1606188026755/current/finalized/subdir19/subdir9/blk_-9223372036824119005
> {code}
>
> The total number of internal blocks deleted during 08:15-08:17 are as follows
> ||internal block||index|| delete num||
> |blk_-9223372036824119008
> blk_-9223372036824119006
> blk_-9223372036824119005
> blk_-9223372036824119004
> blk_-9223372036824119003
> blk_-9223372036824119000 |0
> 2
> 3
> 4
> 5
> 8| 1
> 1
> 1
> 50
> 1
> 1|
>
> {color:#ff0000}During 08:15 to 08:17, we restarted 2 datanode and triggered
> full block report immediately.{color}
>
> There are 2 questions:
> 1. Why are there so many replicas of this block?
> 2. Why delete the internal block with only one copy?
> The reasons for the first problem may be as follows:
> 1. We set the full block report period of some datanode to 168 hours.
> 2. We have done a namenode HA operation.
> 3. After namenode HA, the state of storage became
> {color:#ff0000}stale{color}, and the state not change until next full block
> report.
> 4. The balancer copied the replica without deleting the replica from source
> node, because the source node have the stale storage, and the request was put
> into {color:#ff0000}postponedMisreplicatedBlocks{color}.
> 5. Balancer continues to copy the replica, eventually resulting in multiple
> copies of a replica
> !image-2022-01-10-17-31-35-910.png|width=642,height=269!
> The set of {color:#ff0000}rescannedMisreplicatedBlocks{color} have so many
> block to remove.
> !image-2022-01-10-17-32-56-981.png|width=745,height=124!
> As for the second question, we checked the code of
> {color:#de350b}processExtraRedundancyBlock{color}, but didn't find any
> problem.
>
--
This message was sent by Atlassian Jira
(v8.20.1#820001)
---------------------------------------------------------------------
To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org
For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org
