Walter Su created HDFS-8734:
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Summary: Erasure Coding: one cell need two packets
Key: HDFS-8734
URL: https://issues.apache.org/jira/browse/HDFS-8734
Project: Hadoop HDFS
Issue Type: Sub-task
Reporter: Walter Su
Assignee: Walter Su
The default WritePacketSize is 64k
Currently default cellSize is 64k
We hope one cell consumes one packet. In fact it's not.
By default,
chunkSize = 516( 512 data + 4 checksum)
packetSize = 64k
chunksPerPacket = 126 ( See DFSOutputStream#computePacketChunkSize for details)
numBytes of data in one packet = 64512
cellSize = 65536
When first packet is full ( with 64512 data), there are still 65536 - 64512 =
1024 bytes left.
{code}
super.writeChunk(bytes, offset, len, checksum, ckoff, cklen);
// cell is full and current packet has not been enqueued,
if (cellFull && currentPacket != null) {
enqueueCurrentPacketFull();
}
{code}
When the last 1024 bytes of the cell was written, we meet {{cellFull}} and
create another packet.
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