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https://issues.apache.org/jira/browse/MAPREDUCE-6572?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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John Zhuge updated MAPREDUCE-6572:
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Description:
MAPREDUCE-5899 improves distcp by supporting incremental data copy. That is, if
a file is only appended since it was copied last time, only new data need to be
copied.
This improvement was done before HDFS truncate feature (HDFS-3107) was
implemented. Since we support truncate, if a large file is truncated a little
bit, the whole file will still need to be copied, even with the solution of
MAPREDUCE-5899.
Creating this jira to improve the situation, by possibly remembering the
smallest truncated size, so there is chance to only append from that size on.
HDFS tasks
* Add field *minTruncateLength* to *FileWithSnapshotFeature*, default to file
size.
* Whenever a file is truncated, update the field.
* Pass the field to HDFS client in MODIFY entry of *SnapshotDiffReport*.
CopyMapper tasks
* If *minTruncateLength* < *target_file_length*, CopyMapper should perform a
*truncate(target_file_length - minTruncateLength)* operation.
* If *minTruncateLength* < *source_file_length*, CopyMapper should perform an
*append(source_file_length - minTruncateLength)* operation.
In some cases, CopyMapper may perform a *truncate* followed by an *append*.
was:
MAPREDUCE-5899 improves distcp by supporting incremental data copy. That is, if
a file is only appended since it was copied last time, only new data need to be
copied.
This improvement was done before HDFS truncate feature (HDFS-3107) was
implemented. Since we support truncate, if a large file is truncated a little
bit, the whole file will still need to be copied, even with the solution of
MAPREDUCE-5899.
Creating this jira to improve the situation, by possibly remembering the
smallest truncated size, so there is chance to only append from that size on.
Thanks.
> Improved incremental data copy of distcp for truncated file
> -----------------------------------------------------------
>
> Key: MAPREDUCE-6572
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6572
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Yongjun Zhang
> Assignee: John Zhuge
>
> MAPREDUCE-5899 improves distcp by supporting incremental data copy. That is,
> if a file is only appended since it was copied last time, only new data need
> to be copied.
> This improvement was done before HDFS truncate feature (HDFS-3107) was
> implemented. Since we support truncate, if a large file is truncated a little
> bit, the whole file will still need to be copied, even with the solution of
> MAPREDUCE-5899.
> Creating this jira to improve the situation, by possibly remembering the
> smallest truncated size, so there is chance to only append from that size on.
> HDFS tasks
> * Add field *minTruncateLength* to *FileWithSnapshotFeature*, default to file
> size.
> * Whenever a file is truncated, update the field.
> * Pass the field to HDFS client in MODIFY entry of *SnapshotDiffReport*.
> CopyMapper tasks
> * If *minTruncateLength* < *target_file_length*, CopyMapper should perform a
> *truncate(target_file_length - minTruncateLength)* operation.
> * If *minTruncateLength* < *source_file_length*, CopyMapper should perform an
> *append(source_file_length - minTruncateLength)* operation.
> In some cases, CopyMapper may perform a *truncate* followed by an *append*.
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