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https://issues.apache.org/jira/browse/HDFS-9250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14960038#comment-14960038
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Andrew Wang commented on HDFS-9250:
-----------------------------------
Hi Xiao, thanks for working on this,
So one question about this, we're not supposed to add cached locations that do
not also have a backing disk replica. So in your test case, {{dn}} would be
present in locs already. If I edit your test case to do this, it passes without
the change.
This is probably related to HDFS-8646 which I worked on before, we missed some
places where cache state could get out of sync with replica state. I thought I
added enough pruning to safeguard against this, but maybe I missed a place.
Could you investigate?
> LocatedBlock#addCachedLoc may throw ArrayStoreException when cache is empty
> ---------------------------------------------------------------------------
>
> Key: HDFS-9250
> URL: https://issues.apache.org/jira/browse/HDFS-9250
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: HDFS
> Reporter: Xiao Chen
> Assignee: Xiao Chen
> Attachments: HDFS-9250.001.patch
>
>
> We may see the following exception:
> {noformat}
> java.lang.ArrayStoreException
> at java.util.ArrayList.toArray(ArrayList.java:389)
> at
> org.apache.hadoop.hdfs.protocol.LocatedBlock.addCachedLoc(LocatedBlock.java:205)
> at
> org.apache.hadoop.hdfs.server.namenode.CacheManager.setCachedLocations(CacheManager.java:907)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocationsUpdateTimes(FSNamesystem.java:1974)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocationsInt(FSNamesystem.java:1873)
> {noformat}
> The cause is that in LocatedBlock.java, when {{addCachedLoc}}:
> - Passed in parameter {{loc}}, which is type {{DatanodeDescriptor}}, is added
> to {{cachedList}}
> - {{cachedList}} was assigned to {{EMPTY_LOCS}}, which is type
> {{DatanodeInfoWithStorage}}.
> Both {{DatanodeDescriptor}} and {{DatanodeInfoWithStorage}} are subclasses of
> {{DatanodeInfo}} but do not inherit from each other, resulting in the
> ArrayStoreException.
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