apache/cassandra · error · RuntimeException

Cannot allocated space for a heap dump snapshot. There are…

Error message

Cannot allocated space for a heap dump snapshot. There are only

What it means

HeapUtils.maybeCreateHeapDump requires free disk space of at least twice the JVM max heap (heap dump plus a copy). This RuntimeException is thrown when the FileStore hosting the configured heap dump path has less than 2 * maxMemoryBytes unallocated space, aborting the dump before writing.

Solutions

  1. Free space on the volume holding the heap dump path (delete old hprof files)
  2. Point heap_dump_path / -XX:HeapDumpPath at a volume with at least 2x max heap free
  3. Reduce the heap size if the node is over-allocated relative to disk capacity
  4. Expand the disk/volume used for heap dumps

Example fix

// before (cassandra.yaml): heap_dump_path: /var/lib/cassandra  # volume only 50GB free, 64GB heap
// after (cassandra.yaml):  heap_dump_path: /mnt/dump-volume    # volume with >128GB free
Defensive patterns

Strategy: validation

Validate before calling

long need = 2 * Runtime.getRuntime().maxMemory(); long free = new File(heapDumpPath).getUsableSpace(); if (free < need) logger.error("heap dump path needs {} free bytes, only {} available", need, free);

Try / catch

try { HeapUtils.maybeCreateHeapDump(); } catch (RuntimeException e) { logger.error("Heap dump skipped (disk space): {}", e.getMessage()); }

Prevention

When it happens

Trigger: dump_heap_on_uncaught_exception triggers maybeCreateHeapDump while the disk/volume containing heap_dump_path has freeSpaceBytes < 2 * Runtime.maxMemory(), e.g. a 32GB-heap node dumping to a volume with only 40GB free.

Common situations: Small or nearly-full data volumes used for heap dumps, large heaps (64GB+) on modest disks, heap dump path sharing the Cassandra data disk that is already close to capacity.

Understand the failure class

Background: "File too large" / "file size exceeds limit" errors: why libraries cap file sizes and how to fix them — this error's family across 46 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/c9b786ce9df54aa4. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/utils/HeapUtils.java:118

                if (DatabaseDescriptor.getDumpHeapOnUncaughtException())
                {
                    MBeanServer server = ManagementFactory.getPlatformMBeanServer();

                    Path absoluteBasePath = DatabaseDescriptor.getHeapDumpPath();
                    // We should never reach this point with this value null as we initialize the bool only after confirming
                    // the -XX param / .yaml conf is present on initial init and the JMX entry point, but still worth checking.
                    if (absoluteBasePath == null)
                    {
                        DatabaseDescriptor.setDumpHeapOnUncaughtException(false);
                        throw new RuntimeException("Cannot create heap dump unless -XX:HeapDumpPath or cassandra.yaml:heap_dump_path is specified.");
                    }

                    long maxMemoryBytes = Runtime.getRuntime().maxMemory();
                    long freeSpaceBytes = PathUtils.tryGetSpace(absoluteBasePath, FileStore::getUnallocatedSpace);

                    // Abort if there isn't enough room on the target disk to dump the entire heap and then copy it.
                    if (freeSpaceBytes < 2 * maxMemoryBytes)
                        throw new RuntimeException("Cannot allocated space for a heap dump snapshot. There are only " + freeSpaceBytes + " bytes free at " + absoluteBasePath + '.');

                    HotSpotDiagnosticMXBean mxBean = ManagementFactory.newPlatformMXBeanProxy(server, "com.sun.management:type=HotSpotDiagnostic", HotSpotDiagnosticMXBean.class);
                    String filename = String.format("pid%s-epoch%s.hprof", HeapUtils.getProcessId().toString(), currentTimeMillis());
                    String fullPath = File.getPath(absoluteBasePath.toString(), filename).toString();

                    logger.info("Writing heap dump to {} on partition w/ {} free bytes...", absoluteBasePath, freeSpaceBytes);
                    mxBean.dumpHeap(fullPath, false);
                    logger.info("Heap dump written to {}", fullPath);

                    // Disable further heap dump creations until explicitly re-enabled.
                    DatabaseDescriptor.setDumpHeapOnUncaughtException(false);

                    return fullPath;
                }
            }
            catch (Throwable e)
            {
                logger.warn("Unable to create heap dump.", e);

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