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https://issues.apache.org/jira/browse/HDFS-16214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17505255#comment-17505255
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Xiaoqiao He commented on HDFS-16214:
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Thanks [~zhuxiangyi] for your proposal. It is a great idea. This ticket will
improve deletion more efficient although HDFS-16043 has solved most of issues
for large sub-tree deletion.
I am not sure if it is proper for all situation when release lock for
collection blocks stage.
A. when clean inode being deleted in the set.
B. it seems not only `create file` should be considered, other operations such
as renameTo also need to check, right?
C. what will happen if we delete parent inode during step 2?
D. do you mean the delete logic will be same at Active and Standby side for HA
setup? If that, checkpoint has to wait every deletion complete to checkpoint?
In some corn case, it will postpone checkpoint or if the checkpoint period will
not under control?
Thanks [~zhuxiangyi] for your proposal again.
> Asynchronously collect blocks and update quota when deleting
> ------------------------------------------------------------
>
> Key: HDFS-16214
> URL: https://issues.apache.org/jira/browse/HDFS-16214
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 3.4.0
> Reporter: Xiangyi Zhu
> Assignee: Xiangyi Zhu
> Priority: Major
> Labels: pull-request-available
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> The time-consuming deletion is mainly reflected in three logics , collecting
> blocks, deleting Inode from InodeMap, and deleting blocks. The current
> deletion is divided into two major steps. Step 1 acquires the lock, collects
> the block and inode, deletes the inode, and releases the lock. Step 2 Acquire
> the lock and delete the block to release the lock.
> Phase 2 is currently deleting blocks in batches, which can control the lock
> holding time. Here we can also delete blocks asynchronously.
> Now step 1 still has the problem of holding the lock for a long time.
> For stage 1, we can make the collection block not hold the lock. The process
> is as follows, step 1 obtains the lock, parent.removeChild, writes to
> editLog, releases the lock. Step 2 no lock, collects the block. Step 3
> acquire lock, update quota, release lease, release lock. Step 4 acquire lock,
> delete Inode from InodeMap, release lock. Step 5 acquire lock, delete block
> to release lock.
> There may be some problems following the above process:
> 1. When the /a/b/c file is writing, then delete the /a/b directory. If the
> deletion is performed to the collecting block stage, the client writes
> complete or addBlock to the /a/b/c file at this time. This step is not locked
> and delete /a/b and editLog has been written successfully. In this case, the
> order of editLog is delete /a/c and complete /a/b/c. In this case, the
> standby node playback editLog /a/b/c file has been deleted, and then go to
> complete /a/b/c file will be abnormal.
> *The process is as follows:*
> *write editLog order: delete /a/b/c -> delete /a/b -> complete /a/b/c*
> *replay editLog order:* *delete /a/b/c ->* *delete /a/b ->* *complete /a/b/c
> {color:#ff0000}(not found){color}*
> 2. If a delete operation is executed to the stage of collecting block, then
> the administrator executes saveNameSpace, and then restarts Namenode. This
> situation may cause the Inode that has been deleted from the parent childList
> to remain in the InodeMap.
> To solve the above problem, in step 1, add the inode being deleted to the
> Set. When there is a file WriteFileOp (logAllocateBlockId/logCloseFile
> EditLog), check whether there is this file and one of its parent Inodes in
> the Set, and throw it if there is. An exception FileNotFoundException
> occurred.
> In addition, the execution of saveNamespace needs to wait for all iNodes in
> Set to be removed before execution.
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