apache/druid · error · IllegalArgumentException

druid.indexer.runner.javaOptsArray in context of task: X…

Error message

druid.indexer.runner.javaOptsArray in context of task: X must be an array of strings.

What it means

ForkingTaskRunner allows a task to override the middle manager's Java options via the 'druid.indexer.runner.javaOptsArray' context key. That context value must be an array of strings; if reading/iterating it fails, the runner wraps the cause in IllegalArgumentException naming the task.

Solutions

1. Set druid.indexer.runner.javaOptsArray to a JSON array of strings, e.g. ["-Xmx2g","-XX:+UseG1GC"].
2. If you want a single string, use druid.indexer.runner.javaOpts instead of javaOptsArray.
3. Ensure every element is a string; avoid numeric/boolean entries.

Example fix

// before
"context": {"druid.indexer.runner.javaOptsArray": "-Xmx2g -XX:+UseG1GC"}
// after
"context": {"druid.indexer.runner.javaOptsArray": ["-Xmx2g", "-XX:+UseG1GC"]}

Object opts = task.getContextValue("druid.indexer.runner.javaOptsArray");
if (opts != null && !(opts instanceof List
    && ((List<?>) opts).stream().allMatch(o -> o instanceof String))) {
  throw new IllegalArgumentException("javaOptsArray must be an array of strings");
}

try {
  submitTask(task);
} catch (IllegalArgumentException e) {
  // fix context druid.indexer.runner.javaOptsArray to List<String>
}

When it happens

Trigger: Submitting a task whose context contains druid.indexer.runner.javaOptsArray as a non-array (string, object, number) or an array containing non-string elements; the failure occurs while building the fork command in ForkingTaskRunner.call.

Common situations: Copying a single-string javaOpts value into javaOptsArray without splitting; JSON quoting mistakes in the task context; programmatic builders putting non-string objects into context.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Cannot simultaneously replace and append to existing…
• Conflicting segment granularities found
• Failed to parse metric dimensions and types
• Interval[ ] is empty, must specify a nonempty interval
• Invalid maxLoadFactor

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/fc2adb9a2674929b. Report an issue: GitHub.

Appendix: source

Thrown at indexing-service/src/main/java/org/apache/druid/indexing/overlord/ForkingTaskRunner.java:287

                        Object taskJavaOpts = task.getContextValue(
                            ForkingTaskRunnerConfig.JAVA_OPTS_PROPERTY
                        );
                        if (taskJavaOpts != null) {
                          command.addAll(new QuotableWhiteSpaceSplitter((String) taskJavaOpts));
                        }

                        // Override task specific javaOptsArray
                        try {
                          List<String> taskJavaOptsArray = jsonMapper.convertValue(
                              task.getContextValue(ForkingTaskRunnerConfig.JAVA_OPTS_ARRAY_PROPERTY),
                              new TypeReference<>() {}
                          );
                          if (taskJavaOptsArray != null) {
                            command.addAll(taskJavaOptsArray);
                          }
                        }
                        catch (Exception e) {
                          throw new IllegalArgumentException(
                              ForkingTaskRunnerConfig.JAVA_OPTS_ARRAY_PROPERTY
                              + " in context of task: " + task.getId() + " must be an array of strings.",
                              e
                          );
                        }

                        for (String propName : props.stringPropertyNames()) {
                          for (String allowedPrefix : config.getAllowedPrefixes()) {
                            // See https://github.com/apache/druid/issues/1841
                            if (propName.startsWith(allowedPrefix)
                                && !ForkingTaskRunnerConfig.JAVA_OPTS_PROPERTY.equals(propName)
                                && !ForkingTaskRunnerConfig.JAVA_OPTS_ARRAY_PROPERTY.equals(propName)
                            ) {
                              command.addSystemProperty(propName, props.getProperty(propName));
                            }
                          }
                        }

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