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Hui Fei commented on HDFS-15240: -------------------------------- [~umamaheswararao] Could you please take a look again ? Thanks! > Erasure Coding: dirty buffer causes reconstruction block error > -------------------------------------------------------------- > > Key: HDFS-15240 > URL: https://issues.apache.org/jira/browse/HDFS-15240 > Project: Hadoop HDFS > Issue Type: Bug > Components: datanode, erasure-coding > Reporter: HuangTao > Assignee: HuangTao > Priority: Major > Attachments: HDFS-15240.001.patch, HDFS-15240.002.patch, > HDFS-15240.003.patch, HDFS-15240.004.patch, HDFS-15240.005.patch, > HDFS-15240.006.patch, HDFS-15240.007.patch, HDFS-15240.008.patch, > HDFS-15240.009.patch, HDFS-15240.010.patch, HDFS-15240.011.patch, > image-2020-07-16-15-56-38-608.png, > org.apache.hadoop.hdfs.TestReconstructStripedFile-output.txt, > org.apache.hadoop.hdfs.TestReconstructStripedFile.txt, > test-HDFS-15240.006.patch > > > When read some lzo files we found some blocks were broken. > I read back all internal blocks(b0-b8) of the block group(RS-6-3-1024k) from > DN directly, and choose 6(b0-b5) blocks to decode other 3(b6', b7', b8') > blocks. And find the longest common sequenece(LCS) between b6'(decoded) and > b6(read from DN)(b7'/b7 and b8'/b8). > After selecting 6 blocks of the block group in combinations one time and > iterating through all cases, I find one case that the length of LCS is the > block length - 64KB, 64KB is just the length of ByteBuffer used by > StripedBlockReader. So the corrupt reconstruction block is made by a dirty > buffer. > The following log snippet(only show 2 of 28 cases) is my check program > output. In my case, I known the 3th block is corrupt, so need other 5 blocks > to decode another 3 blocks, then find the 1th block's LCS substring is block > length - 64kb. > It means (0,1,2,4,5,6)th blocks were used to reconstruct 3th block, and the > dirty buffer was used before read the 1th block. > Must be noted that StripedBlockReader read from the offset 0 of the 1th block > after used the dirty buffer. > EDITED for readability. > {code:java} > decode from block[0, 2, 3, 4, 5, 7] to generate block[1', 6', 8'] > Check the first 131072 bytes between block[1] and block[1'], the longest > common substring length is 4 > Check the first 131072 bytes between block[6] and block[6'], the longest > common substring length is 4 > Check the first 131072 bytes between block[8] and block[8'], the longest > common substring length is 4 > decode from block[0, 2, 3, 4, 5, 6] to generate block[1', 7', 8'] > Check the first 131072 bytes between block[1] and block[1'], the longest > common substring length is 65536 > CHECK AGAIN: all 27262976 bytes between block[1] and block[1'], the longest > common substring length is 27197440 # this one > Check the first 131072 bytes between block[7] and block[7'], the longest > common substring length is 4 > Check the first 131072 bytes between block[8] and block[8'], the longest > common substring length is 4{code} > Now I know the dirty buffer causes reconstruction block error, but how does > the dirty buffer come about? > After digging into the code and DN log, I found this following DN log is the > root reason. > {code:java} > [INFO] [stripedRead-1017] : Interrupted while waiting for IO on channel > java.nio.channels.SocketChannel[connected local=/xxxxxxxx:52586 > remote=/xxxxxxxx:50010]. 180000 millis timeout left. > [WARN] [StripedBlockReconstruction-199] : Failed to reconstruct striped > block: BP-714356632-xxxxxxxx-1519726836856:blk_-YYYYYYYYYYYYYY_3472979393 > java.lang.NullPointerException > at > org.apache.hadoop.hdfs.util.StripedBlockUtil.getNextCompletedStripedRead(StripedBlockUtil.java:314) > at > org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedReader.doReadMinimumSources(StripedReader.java:308) > at > org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedReader.readMinimumSources(StripedReader.java:269) > at > org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedBlockReconstructor.reconstruct(StripedBlockReconstructor.java:94) > at > org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedBlockReconstructor.run(StripedBlockReconstructor.java:60) > at > java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) > at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) > at > java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) > at > java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) > at java.base/java.lang.Thread.run(Thread.java:834) {code} > Reading from DN may timeout(hold by a future(F)) and output the INFO log, but > the futures that contains the future(F) is cleared, > {code:java} > return new StripingChunkReadResult(futures.remove(future), > StripingChunkReadResult.CANCELLED); {code} > futures.remove(future) cause NPE. So the EC reconstruction is failed. In the > finally phase, the code snippet in *getStripedReader().close()* > {code:java} > reconstructor.freeBuffer(reader.getReadBuffer()); > reader.freeReadBuffer(); > reader.closeBlockReader(); {code} > free buffer firstly, but the StripedBlockReader still holds the buffer and > write it, that pollute the buffer of BufferPool. -- This message was sent by Atlassian Jira (v8.3.4#803005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org