aeron-io/aeron · error · AeronException

failed to write next session id command

Error message

failed to write next session id command

What it means

DriverProxy.nextAvailableSessionId claims space in the toDriverCommandBuffer to write a GET_NEXT_AVAILABLE_SESSION_ID command so the driver can reserve the next session id for a given stream. tryClaim returned negative because the ring lacked capacity for GetNextAvailableSessionIdMessageFlyweight.LENGTH bytes, so AeronException is thrown and no session id was reserved.

Solutions

1. Verify the media driver is alive and consuming commands
2. Retry nextAvailableSessionId with backoff; capacity returns once the driver drains the queue
3. Reduce the burst of session-id requests; reserve ids lazily per publication
4. Check driver agent thread health (embedded) and enlarge the command ring if saturation is recurring
5. If the driver is confirmed dead, re-establish the Aeron client against a fresh driver

Example fix

// before
int sessionId = driverProxy.nextAvailableSessionId(streamId);
// after
int sessionId;
try {
    sessionId = driverProxy.nextAvailableSessionId(streamId);
} catch (AeronException e) {
    if (!driverProxy.isActive()) throw new IllegalStateException("driver stopped", e);
    Thread.sleep(10);
    sessionId = driverProxy.nextAvailableSessionId(streamId); // retry after drain
}

if (!aeron.context().isDriverActive()) {
    throw new IllegalStateException("driver inactive; nextAvailableSessionId would fail");
}

try {
    int sessionId = driverProxy.nextAvailableSessionId(streamId);
} catch (AeronException e) {
    if (!e.getMessage().startsWith("failed to write")) throw e;
    // brief backoff then retry; abort if driver is confirmed inactive
}

When it happens

Trigger: Calling nextAvailableSessionId(streamId) (used when pre-allocating session ids for exclusive publications) when the client-driver command ring is full: driver dead or stalled, or a burst of control commands saturating the queue.

Common situations: Code reserving many session ids up-front for a set of exclusive publications while the driver is busy or hung; driver process crashed; embedded driver with a blocked agent thread.

Related errors

• failed to write add rcv destination command
• failed to write remove rcv destination command
• failed to write add counter command
• failed to write remove counter command
• failed to write reject image command

AI-assisted analysis of aeron-io/aeron@6d60124e15 (2026-09-12). Data as JSON: /api/errors/bd86417f7f7ea85c. Report an issue: GitHub.

Appendix: source

Thrown at aeron-client/src/main/java/io/aeron/DriverProxy.java:613

            .label(label)
            .typeId(typeId)
            .registrationId(registrationId)
            .correlationId(correlationId)
            .clientId(clientId);

        toDriverCommandBuffer.commit(index);

        return correlationId;
    }

    long nextAvailableSessionId(final int streamId)
    {
        final long correlationId = toDriverCommandBuffer.nextCorrelationId();
        final int index = toDriverCommandBuffer.tryClaim(
            GET_NEXT_AVAILABLE_SESSION_ID, GetNextAvailableSessionIdMessageFlyweight.LENGTH);
        if (index < 0)
        {
            throw new AeronException("failed to write next session id command");
        }

        getNextAvailableSessionIdMessageFlyweight
            .wrap(toDriverCommandBuffer.buffer(), index)
            .streamId(streamId)
            .correlationId(correlationId)
            .clientId(clientId);

        toDriverCommandBuffer.commit(index);

        return correlationId;
    }
}

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