apache/cassandra · warning

User defined function %s ran longer than %dms

Error message

User defined function %s ran longer than %dms

What it means

UDFunction.async logs a warning (and warns the client via ClientWarn) when a user-defined function execution exceeds user_defined_function_warn_timeout milliseconds. Execution is NOT aborted: after warning, the call waits the remaining warn-to-fail window before enforcing the fail timeout.

Source

Thrown at src/java/org/apache/cassandra/cql3/functions/UDFunction.java:512

    }

    private <T> T async(ThreadIdAndCpuTime threadIdAndCpuTime, Callable<T> callable)
    {
        Future<T> future = executor().submit(callable);

        try
        {
            if (DatabaseDescriptor.getUserDefinedFunctionWarnTimeout() > 0)
                try
                {
                    return future.get(DatabaseDescriptor.getUserDefinedFunctionWarnTimeout(), TimeUnit.MILLISECONDS);
                }
                catch (TimeoutException e)
                {

                    // log and emit a warning that UDF execution took long
                    String warn = String.format("User defined function %s ran longer than %dms", this, DatabaseDescriptor.getUserDefinedFunctionWarnTimeout());
                    logger.warn(warn);
                    ClientWarn.instance.warn(warn);
                }

            // retry with difference of warn-timeout to fail-timeout
            return future.get(DatabaseDescriptor.getUserDefinedFunctionFailTimeout() - DatabaseDescriptor.getUserDefinedFunctionWarnTimeout(), TimeUnit.MILLISECONDS);
        }
        catch (InterruptedException e)
        {
            Thread.currentThread().interrupt();
            throw new UncheckedInterruptedException(e);
        }
        catch (ExecutionException e)
        {
            Throwable c = e.getCause();
            if (c instanceof RuntimeException)
                throw (RuntimeException) c;
            throw new RuntimeException(c);
        }

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Optimize or simplify the UDF body
2. Raise user_defined_function_warn_timeout in cassandra.yaml if the runtime is expected
3. Precompute/filter rows before applying the UDF to reduce invocations

Example fix

# cassandra.yaml
# before
user_defined_function_warn_timeout: 500
# after
user_defined_function_warn_timeout: 5000

// Pre-deploy: benchmark the UDF on representative data
long t0 = System.nanoTime(); udf.call(sampleInput); long ms = (System.nanoTime()-t0)/1_000_000;
if (ms > warnTimeout) throw new IllegalStateException("UDF too slow: " + ms + "ms");

When it happens

Trigger: A UDF's future.get() times out at getUserDefinedFunctionWarnTimeout(); invoked via executeAsync or executeAggregateAsync when running a SELECT containing the UDF.

Common situations: UDFs doing expensive per-row computation (regex, crypto, large JSON parsing); JVM pauses; slow sandboxed code on large cells.

Understand the failure class

Background: Request timed out: what client-side request timeouts mean across libraries (Request timed out, TIMED_OUT, APITimeoutError) — this error's family across 39 libraries.

Related errors

• Command '${command}' took too long (${execTime}ms >= ${quota
• Some operations timed out, details available at debug level
• ${executor.name} not terminated
• user_defined_functions_warn_timeout must less than user_defi
• To be able to set enable_user_defined_functions_threads: fal

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/7127df3e40a3be9b. Report an issue: GitHub.