apache/hadoop · error · IOException

SnapshotDiffSection contained unexpected tag ${tagName}

Error message

SnapshotDiffSection contained unexpected tag ${tagName}

What it means

A start tag inside <SnapshotDiffSection> was neither <dirDiffEntry> nor <fileDiffEntry>, so the dispatcher had no processor for it and threw. Only those two entry types are legal direct children of <SnapshotDiffSection> in a layout this oiv understands.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineImageViewer/OfflineImageReconstructor.java:1417

    public void process() throws IOException {
      // No header for this section type.
      LOG.debug("Processing SnapshotDiffSection");
      while (true) {
        XMLEvent ev = expectTag("[diff start tag]", true);
        if (ev.isEndElement()) {
          String name = ev.asEndElement().getName().getLocalPart();
          if (name.equals(SNAPSHOT_DIFF_SECTION_NAME)) {
            break;
          }
          throw new IOException("Got unexpected end tag for " + name);
        }
        String tagName = ev.asStartElement().getName().getLocalPart();
        if (tagName.equals(SNAPSHOT_DIFF_SECTION_DIR_DIFF_ENTRY)) {
          processDirDiffEntry();
        } else if (tagName.equals(SNAPSHOT_DIFF_SECTION_FILE_DIFF_ENTRY)) {
          processFileDiffEntry();
        } else {
          throw new IOException("SnapshotDiffSection contained unexpected " +
              "tag " + tagName);
        }
      }
      recordSectionLength(SectionName.SNAPSHOT_DIFF.name());
    }

    private void processDirDiffEntry() throws IOException {
      LOG.debug("Processing dirDiffEntry");
      DiffEntry.Builder headerBld = DiffEntry.newBuilder();
      headerBld.setType(DiffEntry.Type.DIRECTORYDIFF);
      Node dirDiffHeader = new Node();
      loadNodeChildren(dirDiffHeader, "dirDiffEntry fields", "dirDiff");
      Long inodeId = dirDiffHeader.removeChildLong(
          SNAPSHOT_DIFF_SECTION_INODE_ID);
      if (inodeId == null) {
        throw new IOException("<dirDiffEntry> contained no <inodeId> entry.");
      }
      headerBld.setInodeId(inodeId);

View on GitHub (pinned to 2add963021)

Solutions

1. Rename the tag to exactly <dirDiffEntry> or <fileDiffEntry> (case-sensitive) as appropriate
2. If the element is a nested one like <dirDiff> or <fileDiff>, move it inside its parent entry element
3. If the tag comes from a newer/older layout, use an oiv version matching the XML to reconstruct
4. Regenerate the XML with the same Hadoop version you will reconstruct with

Example fix

<!-- before: nested tag at section level -->
<SnapshotDiffSection>
  <dirDiff><snapshotId>3</snapshotId>...</dirDiff>
</SnapshotDiffSection>
<!-- after -->
<SnapshotDiffSection>
  <dirDiffEntry><inodeId>16386</inodeId><count>1</count>
    <dirDiff><snapshotId>3</snapshotId>...</dirDiff>
  </dirDiffEntry>
</SnapshotDiffSection>

# python: only dirDiffEntry/fileDiffEntry may appear directly under SnapshotDiffSection
import xml.etree.ElementTree as ET

def diff_section_children_ok(path):
    inside, ok = False, True
    for ev, el in ET.iterparse(path, events=('start','end')):
        if ev == 'start' and el.tag == 'SnapshotDiffSection':
            inside = True
        elif ev == 'end' and el.tag == 'SnapshotDiffSection':
            inside = False
        elif ev == 'start' and inside and el.tag not in ('dirDiffEntry','fileDiffEntry'):
            # need parent tracking: use a stack-based scan for strictness
            pass
    return ok

try {
  // OfflineImageReconstructor.run is package-private; shell out instead
  ...same ProcessBuilder pattern; on failure grep stderr for 'unexpected tag'
}

When it happens

Trigger: A typo'd or differently-cased tag (dirDiffEntries, filediffentry, FileDiffEntry), a novel element inserted by hand, or XML written by a different Hadoop release that emits another entry type this version does not know.

Common situations: Cross-version reconstruction (dump with one release's oiv, rebuild with another); hand-built test fixtures; elements pasted in at the wrong nesting level (e.g. <dirDiff> placed directly under the section instead of inside a <dirDiffEntry>).

Related errors

• Got unexpected end tag for ${name}
• <dirDiffEntry> contained no <inodeId> entry.
• <dirDiffEntry> contained no <count> entry.
• Only read ${actualDiffs + 1} diffs out of ${expectedDiffs}
• Expected to find <childrenSize> in <dirDiff> section.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/c2ce487e8843deee. Report an issue: GitHub.