[HBASE-2877] Unnecessary byte written when serializing a Writable RPC parameter

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Not A Problem
• Affects Version/s: 0.20.5, 0.89.20100621, 0.90.0, 0.90.1, 0.90.2, 0.90.3, 0.90.4, 0.90.5, 0.90.6, 0.92.0, 0.92.1, 0.94.0
• Component/s: IPC/RPC
• Hadoop Flags: Incompatible change
• Tags: rpc, ipc
• Assignee: Unassigned
• Reporter: Benoit Sigoure
• Created: 25/Jul/10 22:48
• Updated: 12/Jun/22 00:02
• Resolved: 08/Jun/14 22:01

Description

When HbaseObjectWritable#writeObject serializes a Writable RPC parameter, it writes its "class code" twice to the wire. writeClassCode is already called once unconditionally at the beginning of the method, and for Writable arguments, it's called a second time towards the end of the method. It seems that the code is trying to deal with the "declared type" vs. "actual type" of a parameter. The Hadoop RPC code was already doing this before Stack changed it to use codes in r608738 for HADOOP-2519. It's not documented when this is useful though, and I couldn't find any use case. Every RPC I've seen so far just ends up with the same byte sent twice to the wire.