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https://issues.apache.org/jira/browse/HDFS-10285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16104722#comment-16104722
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Rakesh R commented on HDFS-10285:
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Thanks a lot [~andrew.wang] for the reviews.
bq. Should dfs.storage.policy.satisfier.activate default to false for now?
During NN startup, SPS feature initializes satisfy thread and will stay idle
until user tells to satisfy storage policy for a given path. So, there won't be
much overhead to the Namenode process as the thread will be idle. Also, the
system test report(attached to the jira) and Jenkins unit testing results shows
the feature is stable. Since we have dynamic switch on/off mechanism via
reconfig, I'm OK to disable by default if there is any concern, should I ?
bq. Might also rename this to "enabled" rather than "activate" to align with
other previous config keys.
Agreed, I will raise a sub-task and change the configuration name asap.
bq. What happens during a rolling upgrade? Will DNs ignore the unknown message,
and NN handle this correctly?
Yes, DN will ignore the unknown message. On the othe other side, NN will wait
for certain configured amount of time for the block movement response. After
this period, if there is no response NN will retry scheduling the block
movement. So, no issues with rolling upgrade.
bq. On downgrade, I assume the xattrs just stay there ignored.
Yes, exactly it will be ignored.
> Storage Policy Satisfier in Namenode
> ------------------------------------
>
> Key: HDFS-10285
> URL: https://issues.apache.org/jira/browse/HDFS-10285
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode, namenode
> Affects Versions: HDFS-10285
> Reporter: Uma Maheswara Rao G
> Assignee: Uma Maheswara Rao G
> Attachments: HDFS-10285-consolidated-merge-patch-00.patch,
> HDFS-10285-consolidated-merge-patch-01.patch,
> HDFS-SPS-TestReport-20170708.pdf,
> Storage-Policy-Satisfier-in-HDFS-June-20-2017.pdf,
> Storage-Policy-Satisfier-in-HDFS-May10.pdf
>
>
> Heterogeneous storage in HDFS introduced the concept of storage policy. These
> policies can be set on directory/file to specify the user preference, where
> to store the physical block. When user set the storage policy before writing
> data, then the blocks could take advantage of storage policy preferences and
> stores physical block accordingly.
> If user set the storage policy after writing and completing the file, then
> the blocks would have been written with default storage policy (nothing but
> DISK). User has to run the ‘Mover tool’ explicitly by specifying all such
> file names as a list. In some distributed system scenarios (ex: HBase) it
> would be difficult to collect all the files and run the tool as different
> nodes can write files separately and file can have different paths.
> Another scenarios is, when user rename the files from one effected storage
> policy file (inherited policy from parent directory) to another storage
> policy effected directory, it will not copy inherited storage policy from
> source. So it will take effect from destination file/dir parent storage
> policy. This rename operation is just a metadata change in Namenode. The
> physical blocks still remain with source storage policy.
> So, Tracking all such business logic based file names could be difficult for
> admins from distributed nodes(ex: region servers) and running the Mover tool.
> Here the proposal is to provide an API from Namenode itself for trigger the
> storage policy satisfaction. A Daemon thread inside Namenode should track
> such calls and process to DN as movement commands.
> Will post the detailed design thoughts document soon.
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