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https://issues.apache.org/jira/browse/HDFS-10178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15200464#comment-15200464
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Kihwal Lee commented on HDFS-10178:
-----------------------------------
Datanodes logs something like this:
{noformat}
java.io.IOException: Invalid checksum length: received length is 504 but
expected length is 0
at
org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receivePacket(BlockReceiver.java:586)
at
org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receiveBlock(BlockReceiver.java:895)
at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:804)
at
org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:137)
at
org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:74)
at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:251)
at java.lang.Thread.run(Thread.java:745)
{noformat}
This causes a permanent write failure.
The problem is in {{BlockSender}}. When transferring a block, {{BlockSender}}
gets checksum type from the on-disk meta file.
{code:java}
if (metaIn.getLength() > BlockMetadataHeader.getHeaderSize()) {
...
csum = BlockMetadataHeader.readDataChecksum(checksumIn, block);
...
}
...
if (csum == null) {
csum = DataChecksum.newDataChecksum(DataChecksum.Type.NULL, 512);
}
{code}
Since the code sets the checksum type to {{NULL}} if the on-disk meta file
contains only the header portion, the checksum type during a block transfer is
set incorrectly. When a data packet arrives with checksum, datanode checks
whether it has received the correct amount of checksum data.
{code:java}
final int checksumLen = diskChecksum.getChecksumSize(len);
final int checksumReceivedLen = checksumBuf.capacity();
if (checksumReceivedLen > 0 && checksumReceivedLen != checksumLen) {
throw new IOException("Invalid checksum length: received length is "
+ checksumReceivedLen + " but expected length is " + checksumLen);
}
{code}
The {{getChecksumSize()}} method of {{NULL}} checksum type returns 0, this
check fails.
> Permanent write failures can happen if pipeline recoveries occur for the
> first packet
> -------------------------------------------------------------------------------------
>
> Key: HDFS-10178
> URL: https://issues.apache.org/jira/browse/HDFS-10178
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Kihwal Lee
> Assignee: Kihwal Lee
> Priority: Critical
>
> We have observed that write fails permanently if the first packet doesn't go
> through properly and pipeline recovery happens. If the packet header is sent
> out, but the data portion of the packet does not reach one or more datanodes
> in time, the pipeline recovery will be done against the 0-byte partial block.
>
> If additional datanodes are added, the block is transferred to the new nodes.
> After the transfer, each node will have a meta file containing the header
> and 0-length data block file. The pipeline recovery seems to work correctly
> up to this point, but write fails when actual data packet is resent.
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