seaweedfs/seaweedfs · error · UnsupportedOperationException

Not implemented by the {getSimpleName} FileSystem implementa

Error message

Not implemented by the {getSimpleName} FileSystem implementation

What it means

UnsupportedOperationException thrown unconditionally by SeaweedFileSystem.concat() (seaweed.hdfs.SeaweedFileSystem:338): the Hadoop FileSystem concat operation (append source files onto a target and delete sources atomically) is simply not implemented by this filesystem. Any caller of concat on a seaweedfs:// URI gets this immediately — it is deterministic, not environmental.

Source

Thrown at other/java/hdfs3/src/main/java/seaweed/hdfs/SeaweedFileSystem.java:338

        seaweedFileSystemStore.setPermission(path, permission);
    }

    Path qualify(Path path) {
        return path.makeQualified(uri, workingDirectory);
    }

    /**
     * Concat existing files together.
     *
     * @param trg   the path to the target destination.
     * @param psrcs the paths to the sources to use for the concatenation.
     * @throws IOException                   IO failure
     * @throws UnsupportedOperationException if the operation is unsupported
     *                                       (default).
     */
    @Override
    public void concat(final Path trg, final Path[] psrcs) throws IOException {
        throw new UnsupportedOperationException("Not implemented by the " +
                getClass().getSimpleName() + " FileSystem implementation");
    }

    /**
     * Truncate the file in the indicated path to the indicated size.
     * <ul>
     * <li>Fails if path is a directory.</li>
     * <li>Fails if path does not exist.</li>
     * <li>Fails if path is not closed.</li>
     * <li>Fails if new size is greater than current size.</li>
     * </ul>
     *
     * @param f         The path to the file to be truncated
     * @param newLength The size the file is to be truncated to
     * @return <code>true</code> if the file has been truncated to the desired
     *         <code>newLength</code> and is immediately available to be reused for
     *         write operations such as <code>append</code>, or
     *         <code>false</code> if a background process of adjusting the length of

View on GitHub (pinned to 1c926e8fac)

Solutions

1. Replace concat with copy-based merging: open each source via fs.open, copy bytes into an append/create stream on the target, then fs.delete the sources.
2. If performance matters, do the merge with filesystem-level parallelism or keep files unmerged and merge on read.
3. Longer term: request/implement concat support in the SeaweedFS filer client rather than subclassing to fake it.

Example fix

// before
fs.concat(new Path("/out/merged"), srcPaths); // UnsupportedOperationException

// after — manual merge, then delete sources
try (FSDataOutputStream out = fs.create(new Path("/out/merged"), true)) {
    for (Path src : srcPaths) {
        try (FSDataInputStream in = fs.open(src)) {
            org.apache.hadoop.io.IOUtils.copyBytes(in, out, 1 << 16, false);
        }
    }
}
for (Path src : srcPaths) fs.delete(src, false);

boolean supportsConcat(FileSystem fs) {
    return !(fs instanceof seaweed.hdfs.SeaweedFileSystem)
        && !"seaweedfs".equals(fs.getUri().getScheme());
}

boolean canConcat = !(fs instanceof seaweed.hdfs.SeaweedFileSystem);

try {
    fs.concat(trg, srcs);
} catch (UnsupportedOperationException e) {
    // NOTE: UOE is a RuntimeException — a bare catch(IOException) will NOT stop it
    mergeByCopy(fs, trg, srcs);
}

When it happens

Trigger: Calling fs.concat(trg, psrcs) on a SeaweedFileSystem; higher-level utilities that invoke concat, e.g. FileUtil.concat, distcp/HDFS shell 'hdfs dfs -concat' style flows, or frameworks that merge small part-files via concat (some HBase/MapReduce rollup and file-compaction utilities).

Common situations: Porting HDFS-native pipelines (which rely on cheap concat) to SeaweedFS; data compaction jobs that expect the target's blocks to be reused; tooling upgrades that started calling concat where it previously copied.

Related errors

• Filesystem does not support symlinks!
• Failed to create file: {path}
• Not a directory: {parent}
• Failed to append to file: {path}
• Path is a file: {path}

AI-assisted analysis of seaweedfs/seaweedfs@1c926e8fac (2026-08-15). Data as JSON: /api/errors/7a5db2ad8a63fe2b. Report an issue: GitHub.