MyCATApache/Mycat-Server · error · IOException

Failed to create local dir in $newDir.

Error message

Failed to create local dir in $newDir.

What it means

DataNodeFileManager.getFile() lazily creates per-directory hash subdirectories (hex-formatted subDirId) under a configured local dir. When File.mkdir() fails (and the dir doesn't already exist), it throws IOException 'Failed to create local dir in $newDir.' Note the message uses an uninterpolated Scala-style $newDir token, so it does not show the actual path.

Solutions

1. Verify each configured local dir exists and is writable by the process user before use; create it with mkdirs() at startup
2. Fix filesystem permissions (chown/chmod) or mount the data volume read-write
3. Check disk space and that no regular file occupies the subdirectory path; then retry

Example fix

// before
File dir = new File(localDirs.get(dirId), "%02x".format(String.valueOf(subDirId)));
if (!file.exists() && !file.mkdir()) {
  throw new IOException("Failed to create local dir in $newDir.");
}
// after
File dir = new File(localDirs.get(dirId), "%02x".format(String.valueOf(subDirId)));
dir.getParentFile().mkdirs(); // ensure parent exists
if (!dir.exists() && !dir.mkdirs()) {
  throw new IOException("Failed to create local dir " + dir.getAbsolutePath());
}

File parent = new File(localDir);
if (!parent.isDirectory() || !parent.canWrite()) {
  throw new IllegalStateException("local dir not usable: " + parent);
}
parent.mkdirs();

boolean isUsableDir(File d) { return d != null && d.isDirectory() && d.canWrite(); }

try { manager.getFile(dirId, subDirId); } catch (IOException e) { log.error("cannot create local subdir; check perms/disk/mounts", e); throw e; }

When it happens

Trigger: Calling file()/getFile() (directly or via createTempLocalBlock) when the target subdirectory cannot be created — parent local dir missing, wrong permissions, read-only filesystem, disk full, or a file already exists at the subdirectory path.

Common situations: Misconfigured local dirs pointing to a non-existent or unwritable path; running the process as a user without write permission to the data directory; container with read-only volume mounts; path created by another user with different ownership.

Understand the failure class

Background: mkdir permission denied (EACCES): failed to create directory errors explained — this error's family across 32 libraries.

Related errors

• Failed to delete:
• Failed to list files for dir:
• Mkdirs failed to create
• error while calling spill() on
• error while calling spill() on

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/97028ae4346aa583. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/memory/unsafe/storage/DataNodeFileManager.java:116

  /** Looks up a file by hashing it into one of our local subdirectories. */
  // This method should be kept in sync with
  // org.apache.spark.network.shuffle.ExternalShuffleBlockResolver#getFile().
  public File getFile(String filename) throws IOException {
    // Figure out which local directory it hashes to, and which subdirectory in that
    int hash = JavaUtils.nonNegativeHash(filename);
    int dirId = hash % localDirs.size();
    int subDirId = (hash / localDirs.size()) % subDirsPerLocalDir;

    synchronized (this) {
      File file = subDirs.get(dirId).get(subDirId);
      if (file != null) {
      
      } else {
        file = new File(localDirs.get(dirId), "%02x".format(String.valueOf(subDirId)));
        if (!file.exists() && !file.mkdir()) {
          throw new IOException("Failed to create local dir in $newDir.");
        }
        subDirs.get(dirId).add(subDirId,file);
      }
    }

    /**
     *类似二维数组
     */
    return  new File(subDirs.get(dirId).get(subDirId),filename);
  }

  public File getFile(ConnectionId connid) throws IOException {
    return getFile(connid.name);
  }

  /**TODO config root
   * Create local directories for storing block data. These directories are
   * located inside configured local directories and won't

View on GitHub (pinned to 65f8d8beb7)