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https://issues.apache.org/jira/browse/HDFS-13443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17188607#comment-17188607
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Íñigo Goiri commented on HDFS-13443:
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As discussed in parallel, adding a subcluster (a NameNode) to a path is an
admin operation and shouldn't be that common.
In any case, when adding, if the information is stale, the new data will keep
going to the old locations which is not an issue.
On the other hand, removing a subcluster might be an issue.
Overall, the State Store tracks the version of the mount table each router has
and can lock writes until all routers are up to date.
> RBF: Update mount table cache immediately after changing (add/update/remove)
> mount table entries.
> -------------------------------------------------------------------------------------------------
>
> Key: HDFS-13443
> URL: https://issues.apache.org/jira/browse/HDFS-13443
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: fs
> Reporter: Mohammad Arshad
> Assignee: Mohammad Arshad
> Priority: Major
> Labels: RBF
> Fix For: 3.3.0, HDFS-13891
>
> Attachments: HDFS-13443-012.patch, HDFS-13443-013.patch,
> HDFS-13443-014.patch, HDFS-13443-015.patch, HDFS-13443-016.patch,
> HDFS-13443-017.patch, HDFS-13443-HDFS-13891-001.patch,
> HDFS-13443-HDFS-13891-002.patch, HDFS-13443-branch-2.001.patch,
> HDFS-13443-branch-2.002.patch, HDFS-13443.001.patch, HDFS-13443.002.patch,
> HDFS-13443.003.patch, HDFS-13443.004.patch, HDFS-13443.005.patch,
> HDFS-13443.006.patch, HDFS-13443.007.patch, HDFS-13443.008.patch,
> HDFS-13443.009.patch, HDFS-13443.010.patch, HDFS-13443.011.patch
>
>
> Currently mount table cache is updated periodically, by default cache is
> updated every minute. After change in mount table, user operations may still
> use old mount table. This is bit wrong.
> To update mount table cache, maybe we can do following
> * *Add refresh API in MountTableManager which will update mount table cache.*
> * *When there is a change in mount table entries, router admin server can
> update its cache and ask other routers to update their cache*. For example if
> there are three routers R1,R2,R3 in a cluster then add mount table entry API,
> at admin server side, will perform following sequence of action
> ## user submit add mount table entry request on R1
> ## R1 adds the mount table entry in state store
> ## R1 call refresh API on R2
> ## R1 calls refresh API on R3
> ## R1 directly freshest its cache
> ## Add mount table entry response send back to user.
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