{"record":{"id":"bd86417f7f7ea85c","repo":"aeron-io/aeron","slug":"failed-to-write-next-session-id-command","errorCode":null,"errorMessage":"failed to write next session id command","messagePattern":"failed to write next session id command","errorType":"exception","errorClass":"AeronException","httpStatus":null,"severity":"error","filePath":"aeron-client/src/main/java/io/aeron/DriverProxy.java","lineNumber":613,"sourceCode":"            .label(label)\n            .typeId(typeId)\n            .registrationId(registrationId)\n            .correlationId(correlationId)\n            .clientId(clientId);\n\n        toDriverCommandBuffer.commit(index);\n\n        return correlationId;\n    }\n\n    long nextAvailableSessionId(final int streamId)\n    {\n        final long correlationId = toDriverCommandBuffer.nextCorrelationId();\n        final int index = toDriverCommandBuffer.tryClaim(\n            GET_NEXT_AVAILABLE_SESSION_ID, GetNextAvailableSessionIdMessageFlyweight.LENGTH);\n        if (index < 0)\n        {\n            throw new AeronException(\"failed to write next session id command\");\n        }\n\n        getNextAvailableSessionIdMessageFlyweight\n            .wrap(toDriverCommandBuffer.buffer(), index)\n            .streamId(streamId)\n            .correlationId(correlationId)\n            .clientId(clientId);\n\n        toDriverCommandBuffer.commit(index);\n\n        return correlationId;\n    }\n}\n","sourceCodeStart":595,"sourceCodeEnd":627,"githubUrl":"https://github.com/aeron-io/aeron/blob/6d60124e15e35c11b49ba2e3c2c2858a09a18803/aeron-client/src/main/java/io/aeron/DriverProxy.java#L595-L627","documentation":"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.","triggerScenarios":"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.","commonSituations":"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.","solutions":["Verify the media driver is alive and consuming commands","Retry nextAvailableSessionId with backoff; capacity returns once the driver drains the queue","Reduce the burst of session-id requests; reserve ids lazily per publication","Check driver agent thread health (embedded) and enlarge the command ring if saturation is recurring","If the driver is confirmed dead, re-establish the Aeron client against a fresh driver"],"exampleFix":"// before\nint sessionId = driverProxy.nextAvailableSessionId(streamId);\n// after\nint sessionId;\ntry {\n    sessionId = driverProxy.nextAvailableSessionId(streamId);\n} catch (AeronException e) {\n    if (!driverProxy.isActive()) throw new IllegalStateException(\"driver stopped\", e);\n    Thread.sleep(10);\n    sessionId = driverProxy.nextAvailableSessionId(streamId); // retry after drain\n}","handlingStrategy":"retry","validationCode":"if (!aeron.context().isDriverActive()) {\n    throw new IllegalStateException(\"driver inactive; nextAvailableSessionId would fail\");\n}","typeGuard":null,"tryCatchPattern":"try {\n    int sessionId = driverProxy.nextAvailableSessionId(streamId);\n} catch (AeronException e) {\n    if (!e.getMessage().startsWith(\"failed to write\")) throw e;\n    // brief backoff then retry; abort if driver is confirmed inactive\n}","preventionTips":["Reserve session ids lazily, not in large up-front batches","Verify driver readiness before pre-allocating session ids","Avoid calling during known driver maintenance/stall windows","In embedded setups, keep the driver agent thread responsive","Retry transient claim failures with bounded backoff"],"tags":["aeron","ipc","backpressure","session-id"],"backgroundTag":"command-buffer-full","analyzedSha":"6d60124e15e35c11b49ba2e3c2c2858a09a18803","analyzedAt":"2026-09-12T11:17:07.683Z","contentChangedAt":"2026-09-12T11:17:07.683Z","schemaVersion":2},"datasetVersion":"2026-09-15T23:17:13.987Z"}