[HDFS-14551] NN throws NPE if downgrade it during rolling upgrade from 3.x to 2.x

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Duplicate
• Target Version/s: 2.10.0
• Assignee: Unassigned
• Reporter: Yuxuan Wang
• Created: 06/Jun/19 12:40
• Updated: 19/Aug/19 05:59
• Resolved: 19/Aug/19 05:59

Description

We can downgrade NN during roling upgrade (runned "hdfs dfsadmin -rollingUpgrade prepare) with HDFS-8432 involved. But with HDFS-14172 if the image has any unrecogized section, it will throw IOException at

FSImageFormatProtobuf.java

private void loadInternal(......) {
    ......
    String n = s.getName();
    SectionName sectionName = SectionName.fromString(n);
    if (sectionName == null) {
      throw new IOException("Unrecognized section " + n);
    }
    ......
}

and throw NPE on Hadoop 2.x

FSImageFormatProtobuf.java

private void loadInternal(......) {
    ......
    String n = s.getName();
    switch (sectionName)
    ......
}

When we downgrade NN from 3.x to 2.x, NN may load the image saved by 3.x NN. Then the lack of SectionName.ERASURE_CODING can break 2.x NN.
We should just skip the unrecogized section instead of throwing exception.

Issue Links

• is duplicated by: HDFS-14396 Failed to load image from FSImageFile when downgrade from 3.x to 2.x
• links to: GitHub Pull Request #1128