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https://issues.apache.org/jira/browse/HDFS-404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13263482#comment-13263482
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Li Junjun commented on HDFS-404:
--------------------------------
sorry , in 2 shold be "but has been appended"
I think there are two situations.
1,the file has been swapped with another file,we check the blockId,that's
correct we throw Exceptions!
2,but if the file has not been swapped but has been appended ,we should just
check the blockId ,and should not care about the block's stamp , because in
fact we got the right and updated block list , cause file in hdfs can't be
truncate .
so how about we do it like this ?
if ( oldIter.next().getBlock().getBlockId() !=
newIter.next().getBlock().getBlockId() ) { throw new IOException("Blocklist for
" + src + " has changed!"); }
after all , between two calls to openInfo() the file can be swapped and then
appending,so we should not ignore the under construction file.
> Why open method in class DFSClient would compare old LocatedBlocks and new
> LocatedBlocks?
> -----------------------------------------------------------------------------------------
>
> Key: HDFS-404
> URL: https://issues.apache.org/jira/browse/HDFS-404
> Project: Hadoop HDFS
> Issue Type: Wish
> Reporter: qianyu
> Assignee: Todd Lipcon
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> This is in the package of org.apache.hadoop.hdfs, DFSClient.openInfo():
> if (locatedBlocks != null) {
> Iterator<LocatedBlock> oldIter =
> locatedBlocks.getLocatedBlocks().iterator();
> Iterator<LocatedBlock> newIter =
> newInfo.getLocatedBlocks().iterator();
> while (oldIter.hasNext() && newIter.hasNext()) {
> if (! oldIter.next().getBlock().equals(newIter.next().getBlock())) {
> throw new IOException("Blocklist for " + src + " has changed!");
> }
> }
> }
> Why we need compare old LocatedBlocks and new LocatedBlocks, and in what case
> it happen?
> Why not "this.locatedBlocks = newInfo" directly?
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