apache/pulsar · error · IllegalArgumentException

Window length must be positive [${windowLengthDurationMs}]

Error message

Window length must be positive [${windowLengthDurationMs}]

What it means

Window-function config validation in WindowConfigUtils.validate: a time-based window length (windowLengthDurationMs set alone) was given as zero or negative milliseconds, which cannot define a valid tumbling window; the windowLengthDurationMs value is the faulty input.

Source

Thrown at pulsar-functions/utils/src/main/java/org/apache/pulsar/functions/utils/WindowConfigUtils.java:47

        if (windowConfig.getWindowLengthDurationMs() == null && windowConfig.getWindowLengthCount() == null) {
            throw new IllegalArgumentException("Window length is not specified");
        }

        if (windowConfig.getWindowLengthDurationMs() != null && windowConfig.getWindowLengthCount() != null) {
            throw new IllegalArgumentException(
                    "Window length for time and count are set! Please set one or the other.");
        }

        if (windowConfig.getWindowLengthCount() != null) {
            if (windowConfig.getWindowLengthCount() <= 0) {
                throw new IllegalArgumentException(
                        "Window length must be positive [" + windowConfig.getWindowLengthCount() + "]");
            }
        }

        if (windowConfig.getWindowLengthDurationMs() != null) {
            if (windowConfig.getWindowLengthDurationMs() <= 0) {
                throw new IllegalArgumentException(
                        "Window length must be positive [" + windowConfig.getWindowLengthDurationMs() + "]");
            }
        }

        if (windowConfig.getSlidingIntervalCount() != null) {
            if (windowConfig.getSlidingIntervalCount() <= 0) {
                throw new IllegalArgumentException(
                        "Sliding interval must be positive [" + windowConfig.getSlidingIntervalCount() + "]");
            }
        }

        if (windowConfig.getSlidingIntervalDurationMs() != null) {
            if (windowConfig.getSlidingIntervalDurationMs() <= 0) {
                throw new IllegalArgumentException(
                        "Sliding interval must be positive [" + windowConfig.getSlidingIntervalDurationMs() + "]");
            }
        }

View on GitHub (pinned to 820761864e)

Solutions

Set windowLengthDurationMs to a positive value in milliseconds

Example fix

// before
config.setWindowLengthDurationMs(0L);
// after
config.setWindowLengthDurationMs(60_000L); // 1 minute

Defensive patterns

Strategy: validation

Validate before calling

static void requirePositiveWindowDuration(WindowConfig wc) {
    if (wc.getWindowLengthDurationMs() != null && wc.getWindowLengthDurationMs() <= 0) {
        throw new IllegalArgumentException("windowLengthDurationMs must be > 0, got " + wc.getWindowLengthDurationMs());
    }
}

Type guard

static boolean isValidWindowDurationMs(Long durationMs) {
    return durationMs != null && durationMs > 0;
}

Try / catch

try {
    WindowConfigUtils.validate(windowConfig);
} catch (IllegalArgumentException e) {
    if (e.getMessage() != null && e.getMessage().startsWith("Window length must be positive")) {
        throw new IllegalStateException("Fix window length settings: duration must be a positive number of ms", e);
    }
    throw e;
}

Prevention

To use defaults, omit the duration field instead of setting it to 0.
Double-check unit conversions (seconds vs milliseconds) so values never collapse to 0.
Clamp computed durations with Math.max(1, durationMs) before validation.

When it happens

Trigger: Calling WindowConfigUtils.validate(windowConfig) where getWindowLengthDurationMs() != null and getWindowLengthDurationMs() <= 0 — e.g. setWindowLengthDurationMs(0L), a duration parsed from "0" or an empty unit conversion, or a negative value from subtraction-based logic.

Common situations: Duration computed from (end - start) that evaluated to 0; config placeholders left as 0; unit conversion mistakes (e.g. ms vs seconds producing 0); user entering "0" intending 'use default'.

Understand the failure class

Background: "Invalid configuration value" and "Unsupported/Unknown setting value" errors: why libraries reject your config strings, numbers, and types — this error's family across 30 libraries.

Related errors

AI-assisted analysis of apache/pulsar@820761864e (2026-09-06). Data as JSON: /api/errors/044c5f3bcadf4301. Report an issue: GitHub.