[HADOOP-11626] Comment ReadStatistics to indicate that it tracks the actual read occurred

• Type: Bug
• Status: Patch Available
• Priority: Trivial
• Resolution: Unresolved
• Affects Version/s: 2.6.0
• Target Version/s: 3.5.0
• Assignee: Unassigned
• Reporter: Lei (Eddy) Xu
• Created: 23/Feb/15 23:15
• Updated: 04/Jan/24 11:33

Description

In DFSOutputStream#actualGetFromOneDataNode(), it updates the ReadStatistics even the read is failed:

        int nread = reader.readAll(buf, offset, len);
        updateReadStatistics(readStatistics, nread, reader);

        if (nread != len) {
          throw new IOException("truncated return from reader.read(): " +
                                "excpected " + len + ", got " + nread);
        }

It indicates that ReadStatistics tracks actual read occurred. Need to add comment to ReadStatistics to make this clear.