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https://issues.apache.org/jira/browse/HDFS-2139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16225268#comment-16225268
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feiwei commented on HDFS-2139:
------------------------------
In FsDatasetImpl.java , You should modify to ensure synchronization
public void hardLinkOneBlock(ExtendedBlock srcBlock, ExtendedBlock dstBlock)
throws IOException {
BlockLocalPathInfo blpi = getBlockLocalPathInfo(srcBlock);
File src = new File(blpi.getBlockPath());
File srcMeta = new File(blpi.getMetaPath());
if (getVolume(srcBlock).getAvailable() < dstBlock.getNumBytes()) {
throw new DiskOutOfSpaceException("Insufficient space for hardlink block
" + srcBlock);
}
BlockPoolSlice dstBPS =
getVolume(srcBlock).getBlockPoolSlice(dstBlock.getBlockPoolId());
synchronized (this) {
File dstBlockFile = dstBPS.hardLinkOneBlock(src, srcMeta,
dstBlock.getLocalBlock());
dstBlockFile = dstBPS.addBlock(dstBlock.getLocalBlock(),
dstBlockFile);
ReplicaInfo replicaInfo = new
FinalizedReplica(dstBlock.getLocalBlock(), getVolume(srcBlock),
dstBlockFile.getParentFile());
volumeMap.add(dstBlock.getBlockPoolId(), replicaInfo);
}
}
> Fast copy for HDFS.
> -------------------
>
> Key: HDFS-2139
> URL: https://issues.apache.org/jira/browse/HDFS-2139
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Pritam Damania
> Assignee: Rituraj
> Attachments: HDFS-2139-For-2.7.1.patch, HDFS-2139.patch,
> HDFS-2139.patch
>
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> There is a need to perform fast file copy on HDFS. The fast copy mechanism
> for a file works as
> follows :
> 1) Query metadata for all blocks of the source file.
> 2) For each block 'b' of the file, find out its datanode locations.
> 3) For each block of the file, add an empty block to the namesystem for
> the destination file.
> 4) For each location of the block, instruct the datanode to make a local
> copy of that block.
> 5) Once each datanode has copied over its respective blocks, they
> report to the namenode about it.
> 6) Wait for all blocks to be copied and exit.
> This would speed up the copying process considerably by removing top of
> the rack data transfers.
> Note : An extra improvement, would be to instruct the datanode to create a
> hardlink of the block file if we are copying a block on the same datanode
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