Jinglun created HDFS-14515:
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Summary: The proto type of quota should change to int64.
Key: HDFS-14515
URL: https://issues.apache.org/jira/browse/HDFS-14515
Project: Hadoop HDFS
Issue Type: Improvement
Reporter: Jinglun
Assignee: Jinglun
Attachments: INode.proto, Main.java, NINode.proto
In fsimage.proto, the proto type of quota should be int64 rather than uint64.
In proto, uint64 represents 64 bits unsinged intergers. Since quota in image
could be -1, using uint64 is inappropriate.(see
https://developers.google.com/protocol-buffers/docs/proto#scalar)
HDFS uses uint64 for quota and works fine because the java type corresponding
to uint64 is long, the same as int64. But in c++ and go uint64 and int64 are
mapping to different types. It would be a problem when loading an image with
c++ and fsimage.proto.
The good news is we can simply change uint64 to int64 without breaking any
existing clusters. The two types, int64 and uint64, are serialized
to/deserialized from java long in the same way. Which means a long serialized
to uint64 could be treated as int64 and deserialized to the same long value.
1）long a -> uint64 serialized -> byte[] b -> int64 deserialized -> long c；
2）a == c；
I did a test to show 1 & 2. INode.proto uses uint64 and NINode.proto uses
int64. Main.java shows serializing long as uint64 to byte array and
deserializing the array as int64 to long. Using proto2.5 to compile the proto
files.
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