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https://issues.apache.org/jira/browse/HDFS-6489?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ravi Prakash updated HDFS-6489:
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Attachment: HDFS-6489.007.patch
Andrew! Thanks for the review. Here's a patch with the changes you suggest. I
am sticking with conditional for RBW for now because 1. Its the common case, 2.
RUR doesn't have {{originalBytesReserved}}.
Even with this, {{dfsUsed}} and {{numblocks}} counting is all messed up. e.g.
[FsDatasetImpl.removeOldBlock|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java#L2886]
calls {{decDfsUsedAndNumBlocks}} twice (so even though {{dfsUsed}} is
correctly decremented, {{numBlocks}} is not) . [~brahmareddy], [~vinayrpet] am
I reading this right?
To really get this sorted out, we should probably have a unit test framework
that tests DN side accounting is proper for several different operations (block
creation, appends, block transfer (e.g. from 1 storage to another), etc.).
Unfortunately, I don't think I'll have the cycles for that. Sorry :(
Arpit has seemed amenable to [removing
reservations|https://issues.apache.org/jira/browse/HDFS-9530?focusedCommentId=15248968&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15248968]
if there is some other alternative. I think we should disable the rejection of
writes by DNs based on reservations until we can be sure that our accounting is
correct. Just my $0.02
> DFS Used space is not correct computed on frequent append operations
> --------------------------------------------------------------------
>
> Key: HDFS-6489
> URL: https://issues.apache.org/jira/browse/HDFS-6489
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 2.2.0, 2.7.1, 2.7.2
> Reporter: stanley shi
> Assignee: Weiwei Yang
> Attachments: HDFS-6489.001.patch, HDFS-6489.002.patch,
> HDFS-6489.003.patch, HDFS-6489.004.patch, HDFS-6489.005.patch,
> HDFS-6489.006.patch, HDFS-6489.007.patch, HDFS6489.java
>
>
> The current implementation of the Datanode will increase the DFS used space
> on each block write operation. This is correct in most scenario (create new
> file), but sometimes it will behave in-correct(append small data to a large
> block).
> For example, I have a file with only one block(say, 60M). Then I try to
> append to it very frequently but each time I append only 10 bytes;
> Then on each append, dfs used will be increased with the length of the
> block(60M), not teh actual data length(10bytes).
> Consider in a scenario I use many clients to append concurrently to a large
> number of files (1000+), assume the block size is 32M (half of the default
> value), then the dfs used will be increased 1000*32M = 32G on each append to
> the files; but actually I only write 10K bytes; this will cause the datanode
> to report in-sufficient disk space on data write.
> {quote}2014-06-04 15:27:34,719 INFO
> org.apache.hadoop.hdfs.server.datanode.DataNode: opWriteBlock
> BP-1649188734-10.37.7.142-1398844098971:blk_1073742834_45306 received
> exception org.apache.hadoop.util.DiskChecker$DiskOutOfSpaceException:
> Insufficient space for appending to FinalizedReplica, blk_1073742834_45306,
> FINALIZED{quote}
> But the actual disk usage:
> {quote}
> [root@hdsh143 ~]# df -h
> Filesystem Size Used Avail Use% Mounted on
> /dev/sda3 16G 2.9G 13G 20% /
> tmpfs 1.9G 72K 1.9G 1% /dev/shm
> /dev/sda1 97M 32M 61M 35% /boot
> {quote}
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