Incorrect sorting will cause failure to load an FsImage file

After we have introduced HDFS-14617 or HDFS-14771, when loading an fsimage file, the following error will pop up:
2021-04-15 17:21:17,868 [293072]-INFO [main:FSImage@784]-Planning to load image: FSImageFile(file=/xxxx/hadoop/hdfs/namenode/current/fsimage_000000000xxxx, cpktTxId=000000000xxxx)
2021-04-15 17:25:53,288 [568492]-INFO [main:FSImageFormatPBINode$Loader@229]-Loading 725097952 INodes.
2021-04-15 17:25:53,289 [568493]-ERROR [main:FSImage@730]-Failed to load image from FSImageFile(file=/xxxx/hadoop/hdfs/namenode/current/fsimage_000000000xxxx, cpktTxId=000000000xxxx)
java.lang.IllegalStateException: GLOBAL: serial number 3 does not exist
at org.apache.hadoop.hdfs.server.namenode.SerialNumberMap.get(SerialNumberMap.java:85)
at org.apache.hadoop.hdfs.server.namenode.SerialNumberManager.getString(SerialNumberManager.java:121)
at org.apache.hadoop.hdfs.server.namenode.SerialNumberManager.getString(SerialNumberManager.java:125)
at org.apache.hadoop.hdfs.server.namenode.INodeWithAdditionalFields$PermissionStatusFormat.toPermissionStatus(INodeWithAdditionalFields.java:86)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormatPBINode$Loader.loadPermission(FSImageFormatPBINode.java:93)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormatPBINode$Loader.loadINodeFile(FSImageFormatPBINode.java:303)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormatPBINode$Loader.loadINode(FSImageFormatPBINode.java:280)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormatPBINode$Loader.loadINodeSection(FSImageFormatPBINode.java:237)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormatProtobuf$Loader.loadInternal(FSImageFormatProtobuf.java:237)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormatProtobuf$Loader.load(FSImageFormatProtobuf.java:176)
at org.apache.hadoop.hdfs.server.namenode.FSImageFormat$LoaderDelegator.load(FSImageFormat.java:226)
at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:937)
It was found that this anomaly was related to sorting, as follows:
ArrayList<FileSummary.Section> sections = Lists.newArrayList(summary
.getSectionsList());
Collections.sort(sections, new Comparator<FileSummary.Section>() {
@Override
public int compare(FileSummary.Section s1, FileSummary.Section s2) {
SectionName n1 = SectionName.fromString(s1.getName());
SectionName n2 = SectionName.fromString(s2.getName());
if (n1 == null)

{ return n2 == null? 0: -1; }

else if (n2 == null)

{ return -1; }

else

{ return n1.ordinal()-n2.ordinal(); }

}
});
When n1 != null and n2 == null, this will cause sorting errors.
When loading Sections, the correct order of loading Sections:
NS_INFO -> STRING_TABLE -> INODE
If the sorting is incorrect, the loading order is as follows:
INDOE -> NS_INFO -> STRING_TABLE

Because when loading INODE, you need to rely on STRING_TABLE.