apache/beam · error · IOException

heap_dump.hprof already existed and couldn't be deleted!

Error message

heap_dump.hprof already existed and couldn't be deleted!

What it means

MemoryMonitor.dumpHeap throws this IOException when a previous heap_dump.hprof exists in the target directory and cannot be deleted, blocking creation of a new heap dump. This guards the HotSpotDiagnosticMXBean dump call against writing to a stale or locked file.

Solutions

Delete heap_dump.hprof manually or ensure nothing holds it open, then retry
Point the memory monitor's dump directory at a writable, dedicated location
Serialize dump triggers so only one monitor runs dumpHeap at a time
Check filesystem permissions / mount read-only status of the dump directory

Example fix

// before: fixed filename reused each dump
File fileName = new File(directory, "heap_dump.hprof");
// after: unique per-dump name avoids stale-file conflicts
File fileName = new File(directory,
    "heap_dump_" + System.currentTimeMillis() + ".hprof");

Defensive patterns

Strategy: try-catch

Validate before calling

File dump = new File(dumpDir, "heap_dump.hprof");
boolean writable = dumpDir.canWrite() && (!dump.exists() || dump.delete());

Try / catch

try {
  memoryMonitor.dumpHeap();
} catch (IOException e) {
  logger.warn("heap dump failed: {}", e.getMessage()); // continue without dump
}

Prevention

Use a dedicated, writable dump directory
Clean old hprof files after upload
Serialize dump triggers; don't run multiple monitors

When it happens

Trigger: Triggering a heap dump (e.g. from a memory alarm handler) when heap_dump.hprof already exists in the dump directory and File.delete() fails — typically because the file is locked by another process or the process lacks write permission on it/directory.

Common situations: A previous OOM dump still present and being read/uploaded by another tool; dumping on a read-only or container-mounted volume; two MemoryMonitor instances racing on the same directory; OS file locks (Windows).

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/4a67c5defb3eb89d. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/harness/src/main/java/org/apache/beam/fn/harness/status/MemoryMonitor.java:649

  }

  /**
   * Dump the current heap profile to a file in the given directory and return its name.
   *
   * <p>NOTE: We deliberately don't salt the heap dump filename so as to minimize disk impact of
   * repeated dumps. These files can be of comparable size to the local disk.
   */
  private static synchronized File dumpHeap(File directory)
      throws MalformedObjectNameException,
          InstanceNotFoundException,
          ReflectionException,
          MBeanException,
          IOException {

    boolean liveObjectsOnly = false;
    File fileName = new File(directory, "heap_dump.hprof");
    if (fileName.exists() && !fileName.delete()) {
      throw new IOException("heap_dump.hprof already existed and couldn't be deleted!");
    }

    MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
    ObjectName oname = new ObjectName("com.sun.management:type=HotSpotDiagnostic");
    Object[] parameters = {fileName.getPath(), liveObjectsOnly};
    String[] signatures = {String.class.getName(), boolean.class.getName()};
    mbs.invoke(oname, "dumpHeap", parameters, signatures);

    if (java.nio.file.FileSystems.getDefault().supportedFileAttributeViews().contains("posix")) {
      Files.setPosixFilePermissions(
          fileName.toPath(),
          ImmutableSet.of(
              PosixFilePermission.OWNER_READ,
              PosixFilePermission.GROUP_READ,
              PosixFilePermission.OTHERS_READ));
    } else {
      fileName.setReadable(true, true);
    }

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