HDFS-17732. addExpectedReplicasToPending should add EC block expectedStorages in PendingReconstructionBlocks. #7414
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slfan1989
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@zhangshuyan0 Could you please review this PR? Thank you very much! |
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…Storages in PendingReconstructionBlocks
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@Hexiaoqiao @ZanderXu @tomscut , Hello Sir , please reivew this PR if you have time . Thanks very much |
slfan1989
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@LiuGuH Thanks for the contribution! I'm not good at EC, but I asked for help from other members. |
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Description of PR
JIRA: HDFS-17732. addExpectedReplicasToPending should add EC block expectedStorages in PendingReconstructionBlocks.
Now when a block commit , it should add expectedStorages into PendingReconstructionBlocks if datanode ibr is not sent from expected locations. And for a ec block group , only blkStriped.getRealTotalBlockNum() == expectedStorages.length will be added into PendingReconstructionBlocks.
The problem is that when an ec file size <= ecPolicy.getCellSize *(ecPolicy.getNumDataUnits()-1), it always will be blkStriped.getRealTotalBlockNum() < expectedStorages.length. This will lead to namenode generation reconstruction task first if other ibrs comme later.
For example:
(1) A EC file with XOR-2-1-1024k，file size <=1024k
(2) The file has one ec block and 3 replics (blk0,blk1,blk2) , and only blk0,blk2 has data because of file size <=1024k
(3) Namenode recived IBR0
(4) Client close file, now the file reach MinStorage and ec block commit
(5) Now blkStriped.getRealTotalBlockNum()=1 expectedStorages.length=3 ,so blk1,blk2 cannot add into PendingReconstructionBlocks
(6) Ec block complete and file close, because it has missing block so add into neededReconstruction
(7) Namenode generation ec reconstruction task and deliver to the datanode DN2
(8) Namenode recived IBR2 (DN2 blk2)
(9) Namenode recived new block (DN2 ec reconstruction task blk2')
(10) For ecPolicy, DN2 has two block blk2 ,blk2' , this increases the risk of data loss
(11) For other ecPolicy, on a same datanode may has two different replicas on one ec block group , and namenode will only record the later replica.
So the right way is:
(1) addExpectedReplicasToPending should add EC block expectedStorages in PendingReconstructionBlocks
(2) In order to reduce PendingReconstructionBlocks timeout, when a file close or ibr commes, we should remove block which has enough replicas from PendingReconstructionBlocks