apache/flink · critical · IOException

Unrecognized version: {}

Error message

Unrecognized version: {}

What it means

Thrown by SimpleTypeSerializerSnapshot.readSnapshot in its default switch branch. The snapshot format only recognizes readVersion 2 (legacy, with a class-name field that is read and discarded) and readVersion 3 (current, no payload). Any other version indicates the snapshot was written by an incompatible format revision or the data is corrupt.

Source

Thrown at flink-core/src/main/java/org/apache/flink/api/common/typeutils/SimpleTypeSerializerSnapshot.java:110

    }

    @Override
    public void readSnapshot(int readVersion, DataInputView in, ClassLoader classLoader)
            throws IOException {
        switch (readVersion) {
            case 3:
                {
                    break;
                }
            case 2:
                {
                    // we don't need the classname any more; read and drop to maintain compatibility
                    in.readUTF();
                    break;
                }
            default:
                {
                    throw new IOException("Unrecognized version: " + readVersion);
                }
        }
    }

    // ------------------------------------------------------------------------
    //  standard utilities
    // ------------------------------------------------------------------------

    @Override
    public final boolean equals(Object obj) {
        return obj != null && obj.getClass() == getClass();
    }

    @Override
    public final int hashCode() {
        return getClass().hashCode();
    }

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Restore the checkpoint with the Flink version that created it, then take a fresh savepoint and migrate.
2. Check the Flink release notes for state backward-compatibility guarantees between your source and target versions.
3. If the data is corrupt rather than version-incompatible, re-create the checkpoint from a known-good state.

// Verify the Flink version supports the snapshot version in your checkpoints
// SimpleTypeSerializerSnapshot supports readVersion 2 and 3 only (version 1 is pre-1.7.x)

try {
    backend.restore(checkpointPath);
} catch (IOException e) {
    if (e.getMessage().contains("Unrecognized version")) {
        log.error("Snapshot version not supported by this Flink version.");
    }
    throw e;
}

When it happens

Trigger: Restoring a checkpoint that contains a SimpleTypeSerializerSnapshot written with a version other than 2 or 3. Version 1 is reserved for the legacy ParameterlessTypeSerializerConfig and is not handled here. A version above 3 would come from a future or forked Flink. Corrupt data can also produce an arbitrary version integer.

Common situations: Restoring a very old savepoint (pre-1.7.x, version 1) on a modern Flink. Restoring a checkpoint from a newer/custom Flink fork that bumped CURRENT_VERSION. Corrupted snapshot bytes where the version field holds garbage.

Related errors

• Unrecognized version: {}
• Unrecognized version for TypeSerializerSnapshot format: {}
• Corrupt data, magic number mismatch. Expected %8x, found %8x
• Corrupt data, magic number mismatch. Expected %8x, found %8x
• This object is a dummy TypeSerializer.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/ccaec600851415e5. Report an issue: GitHub.