CapMoon opened a new pull request, #8462:
URL: https://github.com/apache/hadoop/pull/8462
HDFS-17913. Dead DataNode in Host2NodesMap can break block location sorting
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### Description of PR
When HeartbeatManager#heartbeatCheck removes a dead DataNode via
DatanodeManager#removeDeadDatanode, the node is removed from NetworkTopology,
but it may still be returned by host2DatanodeMap.
If an HDFS client is co-located on the same host/IP as that dead DataNode,
DatanodeManager#sortLocatedBlock may treat the client as a DataNode reader.
Since the descriptor has already been removed from NetworkTopology, its parent
is null, and NetworkTopology#sortByDistance can compute incorrect weights for
replicas. This may cause rack locality to be lost, especially when
dfs.namenode.read.considerLoad=true.
Expected behavior:
A DataNode descriptor detached from NetworkTopology should not be treated as
a DataNode reader.
Proposed fix:
In DatanodeManager#sortLocatedBlock, ignore a host-map hit whose topology
parent is null
### How was this patch tested?
Tested in unit test
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