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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-6346) Optimize OP_SET_XATTRS by persisting single Xattr entry per setXattr api call
Date Wed, 07 May 2014 07:48:21 GMT
Uma Maheswara Rao G created HDFS-6346:
-----------------------------------------

             Summary: Optimize OP_SET_XATTRS by persisting single Xattr entry per setXattr
api call
                 Key: HDFS-6346
                 URL: https://issues.apache.org/jira/browse/HDFS-6346
             Project: Hadoop HDFS
          Issue Type: Sub-task
          Components: namenode
            Reporter: Uma Maheswara Rao G


When a new xattrs set on an Inode, it may add this with OP_SET_XATTRS and let's say [USER.name1:value1]
On a next call if we set another xattrs, then it may store along with older existing xattrs
again. It may be like [USER.name1:value1, USER.name2:value2]
So, on adding more xattrs on same Inode, that list may grow and we keep store the entries
of already existing name, value fairs.
Right now we defaulted the max Xattrs on an Inode to 32 and configured. If user modified it
to much larger value and start setting xattrs, then edits loading may create issue like my
above example.
But I didn't refer any usecase of having large number of xattrs, this is just the assumption
to consider a case. My biggest doubt is whether we will have such real usecases to have huge
xattrs on a single INode.
So, here is a thought on having OP_SET_XATTR for each setXAttr operation to be logged, When
we replay them we need to consolidate. This is some initial thought we can think more if others
also feel we need to consider this case to handle.

Otherwise we endup storing Xattrs entries in editlog file as n(n+1)/2 where n is number xattrs
for a file/dir. This may be issue only when we have large number configured max xattrs for
inode.



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