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From "Manoj Govindassamy (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-11435) NameNode should track open for write files lengths more frequent than on newer block allocations
Date Tue, 21 Feb 2017 04:22:44 GMT
Manoj Govindassamy created HDFS-11435:
-----------------------------------------

             Summary: NameNode should track open for write files lengths more frequent than
on newer block allocations
                 Key: HDFS-11435
                 URL: https://issues.apache.org/jira/browse/HDFS-11435
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Manoj Govindassamy
            Assignee: Manoj Govindassamy


*Problem:*
Currently the length of an open for write / Under construction file is updated on the NameNode
only when 

# Block boundary: On block boundaries and upon allocation of new Block, NameNode gets to know
the file growth and the file length catches up
# hsync(SyncFlag.UPDATE_LENGTH): Upon Client apps invoking a hsync on the write stream with
a special flag, DataNodes send an incremental block report with the latest file length which
NameNode uses it to update its meta data.
# First hflush() on the new Block: Upon Client apps doing first time hflush() on an every
new Block, DataNodes notifies NameNode about the latest file length.
# Output stream close: Forces DataNodes update NameNode about the file length after data persistence
and proper acknowledgements in the pipeline.

So, lengths for open for write files are usually a lot less than the length seen by the DN/client.
Highly preferred to have NameNode not lagging in file lengths by order of Block size for under
construction files and to have more frequent, scalable update mechanism for these open file
lengths. 




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