SolaceIO.Write: Overriding PUB_ACK_WINDOW_SIZE to

Error message

SolaceIO.Write: Overriding PUB_ACK_WINDOW_SIZE to {} since LOWER_LATENCY mode was selected

What it means

INFO-level warning logged by the Solace SessionService when LOWER_LATENCY write mode is selected but the user had explicitly set a PUB_ACK_WINDOW_SIZE. The connector overrides the user's value with the latency-optimized default in LOWER_LATENCY mode, and this log documents the override so the behavior change is not a surprise.

Solutions

Accept the override or use SubmissionMode.CUSTOM to keep your own window size.
Remove the explicit PUB_ACK_WINDOW_SIZE setting to silence the warning.
Verify throughput/latency behavior after the override in a test pipeline.

Example fix

// before
props.setProperty(JCSMPProperties.PUB_ACK_WINDOW_SIZE, 255);
.withSubmissionMode(SubmissionMode.LOWER_LATENCY);
// after
.withSubmissionMode(SubmissionMode.CUSTOM); // keeps user window

Defensive patterns

Strategy: validation

Validate before calling

Integer ackWindow = (Integer) props.getProperty(JCSMPProperties.PUB_ACK_WINDOW_SIZE);
if (mode == SubmissionMode.LOWER_LATENCY && ackWindow != null && ackWindow != STREAMING_PUB_ACK_WINDOW) {
  LOG.warn("PUB_ACK_WINDOW_SIZE=" + ackWindow + " will be overridden to " + STREAMING_PUB_ACK_WINDOW);
}

Prevention

Verify effective session properties in an integration test before production.
Use CUSTOM mode to preserve any explicitly tuned ack window.
Log resolved properties at pipeline startup for audit.

When it happens

Trigger: write().withSubmissionMode(LOWER_LATENCY) with an explicit PUB_ACK_WINDOW_SIZE other than STREAMING_PUB_ACK_WINDOW.

Common situations: Custom ack-window tuning colliding with a built-in submission mode preset.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/5dcbfd61bd04838b. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/io/solace/src/main/java/org/apache/beam/sdk/io/solace/broker/SessionService.java:251

        // Override the properties
        // Use a dedicated thread for callbacks, increase the ack window size
        props.setProperty(JCSMPProperties.MESSAGE_CALLBACK_ON_REACTOR, false);
        props.setProperty(JCSMPProperties.PUB_ACK_WINDOW_SIZE, BATCHED_PUB_ACK_WINDOW);
        LOG.info(
            "SolaceIO.Write: Using HIGHER_THROUGHPUT mode, MESSAGE_CALLBACK_ON_REACTOR is FALSE,"
                + " PUB_ACK_WINDOW_SIZE is {}",
            BATCHED_PUB_ACK_WINDOW);
        break;
      case LOWER_LATENCY:
        // Check if it was set by user, show override warning
        if (msgCbProp != null && !msgCbProp) {
          LOG.warn(
              "SolaceIO.Write: Overriding MESSAGE_CALLBACK_ON_REACTOR to true since"
                  + " LOWER_LATENCY mode was selected");
        }

        if ((ackWindowSize != null && ackWindowSize != STREAMING_PUB_ACK_WINDOW)) {
          LOG.warn(
              "SolaceIO.Write: Overriding PUB_ACK_WINDOW_SIZE to {} since"
                  + " LOWER_LATENCY mode was selected",
              STREAMING_PUB_ACK_WINDOW);
        }

        // Override the properties
        // Send from the same thread where the produced is being called. This offers the lowest
        // latency, but a low throughput too.
        props.setProperty(JCSMPProperties.MESSAGE_CALLBACK_ON_REACTOR, true);
        props.setProperty(JCSMPProperties.PUB_ACK_WINDOW_SIZE, STREAMING_PUB_ACK_WINDOW);
        LOG.info(
            "SolaceIO.Write: Using LOWER_LATENCY mode, MESSAGE_CALLBACK_ON_REACTOR is TRUE,"
                + " PUB_ACK_WINDOW_SIZE is {}",
            STREAMING_PUB_ACK_WINDOW);

        break;
      case CUSTOM:
        LOG.info(

View on GitHub (pinned to 12126d8942)