Rajesh Balamohan created HIVE-11945:
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Summary: ORC with non-local reads may not be reusing connection to
DN
Key: HIVE-11945
URL: https://issues.apache.org/jira/browse/HIVE-11945
Project: Hive
Issue Type: Bug
Reporter: Rajesh Balamohan
Assignee: Rajesh Balamohan
When “seek + readFully(buffer, offset, length)” is used, DFSInputStream ends
up going via “readWithStrategy()”. This sets up BlockReader with length
equivalent to that of the block size. So until this position is reached,
RemoteBlockReader2.peer would not be added to the PeerCache (Plz refer
RemoteBlockReader2.close() in HDFS). So eventually the next call to the same
DN would end opening a new socket. In ORC, when it is not a data local read,
this has a the possibility of opening/closing lots of connections with DN.
In random reads, it would be good to set this length to the amount f data that
is to be read (e.g pread call in DFSInputStream which sets up the BlockReader’s
length correctly & the code path returns the Peer back to peer cache properly).
“readFully(position, buffer, offset, length)” follows this code path and ends
up reusing the connections properly. Creating this JIRA to fix this issue.
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