apache/hadoop · error · IOException

Expected to find <childrenSize> in <dirDiff> section.

Error message

Expected to find <childrenSize> in <dirDiff> section.

What it means

A <dirDiff> element is missing <childrenSize>, which the protobuf DirectoryDiff requires (it is a mandatory field, unlike the optional <snapshotId> and <name> read just before it). removeChildInt on the loaded dirDiff node returned null, so reconstruction aborts for this diff.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineImageViewer/OfflineImageReconstructor.java:1463

        try {
          expectTag(SNAPSHOT_DIFF_SECTION_DIR_DIFF, false);
        } catch (IOException e) {
          throw new IOException("Only read " + (actualDiffs + 1) +
              " diffs out of " + expectedDiffs, e);
        }
        Node dirDiff = new Node();
        loadNodeChildren(dirDiff, "dirDiff fields");
        FsImageProto.SnapshotDiffSection.DirectoryDiff.Builder bld =
            FsImageProto.SnapshotDiffSection.DirectoryDiff.newBuilder();
        Integer snapshotId = dirDiff.removeChildInt(
            SNAPSHOT_DIFF_SECTION_SNAPSHOT_ID);
        if (snapshotId != null) {
          bld.setSnapshotId(snapshotId);
        }
        Integer childrenSize = dirDiff.removeChildInt(
            SNAPSHOT_DIFF_SECTION_CHILDREN_SIZE);
        if (childrenSize == null) {
          throw new IOException("Expected to find <childrenSize> in " +
              "<dirDiff> section.");
        }
        bld.setIsSnapshotRoot(dirDiff.removeChildBool(
            SNAPSHOT_DIFF_SECTION_IS_SNAPSHOT_ROOT));
        bld.setChildrenSize(childrenSize);
        String name = dirDiff.removeChildStr(SECTION_NAME);
        if (name != null) {
          bld.setName(ByteString.copyFrom(name, StandardCharsets.UTF_8));
        }
        Node snapshotCopy = dirDiff.removeChild(
            SNAPSHOT_DIFF_SECTION_SNAPSHOT_COPY);
        if (snapshotCopy != null) {
          bld.setSnapshotCopy(createINodeDirectoryBuilder(snapshotCopy));
        }
        Integer expectedCreatedListSize = dirDiff.removeChildInt(
            SNAPSHOT_DIFF_SECTION_CREATED_LIST_SIZE);
        if (expectedCreatedListSize == null) {
          throw new IOException("Expected to find <createdListSize> in " +

View on GitHub (pinned to 2add963021)

Solutions

1. Add <childrenSize>N</childrenSize> to the affected <dirDiff> (the directory's children count in that snapshot; 0 is valid)
2. Check spelling, case, and nesting - it must be a direct child of <dirDiff>
3. Regenerate the XML from the original fsimage with a same-version oiv to recover the true values
4. Pre-scan for <dirDiff> elements lacking required children before running ReverseXML

Example fix

<!-- before -->
<dirDiff><snapshotId>3</snapshotId><name>snap1</name></dirDiff>
<!-- after -->
<dirDiff><snapshotId>3</snapshotId><childrenSize>0</childrenSize><name>snap1</name></dirDiff>

# python: every <dirDiff> needs <childrenSize>
import xml.etree.ElementTree as ET

def dirdiffs_have_childrensize(path):
    for ev, el in ET.iterparse(path, events=('end',)):
        if el.tag == 'dirDiff' and el.find('childrenSize') is None:
            return False
    return True

// oiv exit != 0 with 'Expected to find <childrenSize>' -> patch the named
// <dirDiff>, delete partial output, retry

When it happens

Trigger: A <dirDiff> hand-authored or trimmed without <childrenSize>, or the field renamed/misspelled (exact tag 'childrenSize' required); also fields accidentally nested inside <snapshotCopy> during restructuring.

Common situations: Hand-written diffs copied from a template that omitted the field; scripts emitting only the 'interesting' fields; XML from an older writer that predates the field.

Related errors

• <dirDiffEntry> contained no <inodeId> entry.
• <dirDiffEntry> contained no <count> entry.
• Expected to find <createdListSize> in <dirDiff> section.
• Expected <created> entry to have a <name> field
• <fileDiffEntry> contained no <inodeid> entry.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/83ce5ec72e075e6a. Report an issue: GitHub.