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https://issues.apache.org/jira/browse/HDFS-9146?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tsz Wo Nicholas Sze updated HDFS-9146:
--------------------------------------
Component/s: (was: HDFS)
hdfs-client
> HDFS forward seek() within a block shouldn't spawn new TCP
> Peer/RemoteBlockReader
> ---------------------------------------------------------------------------------
>
> Key: HDFS-9146
> URL: https://issues.apache.org/jira/browse/HDFS-9146
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.6.0, 2.8.0, 2.7.1
> Reporter: Gopal V
>
> When a seek() + forward readFully() is triggered from a remote dfsclient,
> HDFS opens a new remote block reader even if the seek is within the same HDFS
> block.
> (analysis from [~rajesh.balamohan])
> This is due to the fact that a simple read operation assumes that the user is
> going to read till the end of the block.
> {code}
> try {
> blockReader = getBlockReader(targetBlock, offsetIntoBlock,
> targetBlock.getBlockSize() - offsetIntoBlock, targetAddr,
> storageType, chosenNode);
> {code}
> https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java#L624
> Since the user hasn't read till the end of the block when the next seek
> happens, the BlockReader assumes this is an aborted read and tries to throw
> away the TCP peer it has got.
> https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/RemoteBlockReader2.java#L324
> {code}
> // If we've now satisfied the whole client read, read one last packet
> // header, which should be empty
> if (bytesNeededToFinish <= 0) {
> readTrailingEmptyPacket();
> ...
> sendReadResult(Status.SUCCESS);
> {code}
> Since that is not satisfied, the status code is unset & the peer is not
> returned to the cache.
> {code}
> if (peerCache != null && sentStatusCode) {
> peerCache.put(datanodeID, peer);
> } else {
> peer.close();
> }
> {code}
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