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https://issues.apache.org/jira/browse/HDFS-12911?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16291186#comment-16291186
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Uma Maheswara Rao G commented on HDFS-12911:
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[~chris.douglas], Thank you for all the valuable suggestions. We are working on
to reduce the lock and other optimizations. For lock improvement, [~rakeshr]
is almost ready with Patch. Once tested he will post.
For the above mem optimizations, I am trying to profile.
Some updates:
For UMA.2: Actually we are storing the matters in Feature as byte array. So,
having just Xattr created obj static and reusing will not give benefit, that
could reduce obj for GC though. Another improvement could be creating buffer
pool and reuse, as when new Xattr added, it is removing the existing added
feature and adding again. However, reducing xattr key name will have less space
occupied.
Overall with my perf number locally shows no significant growth because of SPS.
For 5 million filed up SPS calls, it is approximately taking 240MB ( for front
Q and Xattr). After few of above improvement, it could reduce further. Also,
IMO, 5 million directories means, it could cover whole cluster as users most
preferably call SPS on directories where storage policy set. Consuming from
front Q is throttled, so memory will be fixed from that part of processing.
> [SPS]: Fix review comments from discussions in HDFS-10285
> ---------------------------------------------------------
>
> Key: HDFS-12911
> URL: https://issues.apache.org/jira/browse/HDFS-12911
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, namenode
> Reporter: Uma Maheswara Rao G
> Assignee: Rakesh R
> Attachments: HDFS-12911.00.patch
>
>
> This is the JIRA for tracking the possible improvements or issues discussed
> in main JIRA
> So far comments to handle
> Daryn:
> # Lock should not kept while executing placement policy.
> # While starting up the NN, SPS Xattrs checks happen even if feature
> disabled. This could potentially impact the startup speed.
> UMA:
> # I am adding one more possible improvement to reduce Xattr objects
> significantly.
> SPS Xattr is constant object. So, we create one Xattr deduplication object
> once statically and use the same object reference when required to add SPS
> Xattr to Inode. So, here additional bytes required for storing SPS Xattr
> would turn to same as single object ref ( i.e 4 bytes in 32 bit). So Xattr
> overhead should come down significantly IMO. Lets explore the feasibility on
> this option.
> Xattr list Future will not be specially created for SPS, that list would have
> been created by SetStoragePolicy already on the same directory. So, no extra
> Feature creation because of SPS alone.
> # Currently SPS putting long id objects in Q for tracking SPS called Inodes.
> So, it is additional created and size of it would be (obj ref + value) = (8 +
> 8) bytes [ ignoring alignment for time being]
> So, the possible improvement here is, instead of creating new Long obj, we
> can keep existing inode object for tracking. Advantage is, Inode object
> already maintained in NN, so no new object creation is needed. So, we just
> need to maintain one obj ref. Above two points should significantly reduce
> the memory requirements of SPS. So, for SPS call: 8bytes for called inode
> tracking + 8 bytes for Xattr ref.
> # Use LightWeightLinkedSet instead of using LinkedList for from Q. This will
> reduce unnecessary Node creations inside LinkedList.
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