{"record":{"id":"54d82baaf8876e2e","repo":"influxdata/influxdb","slug":"another-process-has-written-to-the-wal-ahead-of-this-one","errorCode":null,"errorMessage":"another process has written to the WAL ahead of this one","messagePattern":"another process has written to the WAL ahead of this one","errorType":"exception","errorClass":"WalBufferErrorState","httpStatus":null,"severity":"critical","filePath":"influxdb3_wal/src/object_store.rs","lineNumber":852,"sourceCode":"        self.state = state;\n    }\n\n    fn is_accepting_writes(&self) -> bool {\n        matches!(self.state, WalBufferState::AcceptingWrites)\n    }\n}\n\n#[derive(Debug, Default, Copy, Clone)]\nenum WalBufferState {\n    #[default]\n    AcceptingWrites,\n    ShuttingDown,\n    Error(WalBufferErrorState),\n}\n\n#[derive(Debug, thiserror::Error, Copy, Clone)]\nenum WalBufferErrorState {\n    #[error(\"another process has written to the WAL ahead of this one\")]\n    WalAlreadyWrittenTo,\n}\n\n// Writes should only fail if the underlying WAL throws an error. They are validated before they\n// are buffered. The WAL should continuously retry the write until it succeeds. But if a timeout\n// passes, we can use this to pass the object store error back to the client.\n#[derive(Debug, Clone)]\npub enum WriteResult {\n    Success(()),\n    Error(String),\n}\n\nimpl WalBuffer {\n    fn write_ops_unconfirmed(&mut self, ops: Vec<WalOp>) -> crate::Result<(), crate::Error> {\n        if !self.is_accepting_writes() {\n            return Err(crate::Error::Shutdown);\n        }\n        if self.op_count >= self.op_limit {","sourceCodeStart":834,"sourceCodeEnd":870,"githubUrl":"https://github.com/influxdata/influxdb/blob/06200ef96ba82c5f6727e5038a83af8e722c6875/influxdb3_wal/src/object_store.rs#L834-L870","documentation":"WalBufferErrorState::WalAlreadyWrittenTo is a buffered-write error set when the WAL discovers that a file it was about to write already exists on the object store at the expected sequence position — i.e. another writer has advanced the WAL ahead of this one. The buffer flips into the Error state, stops accepting new writes, and pending write callers receive 'another process has written to the WAL ahead of this one'. The library deliberately halts rather than corrupting the sequence.","triggerScenarios":"During flush/rotation, the object-store put fails with Error::AlreadyExists for a WAL file path this writer did not write (object_store.rs:366-383); the flush buffer then latches WalAlreadyWrittenTo and returns this message to all waiting and subsequent writes.","commonSituations":"Two influxdb3 processes started with the same --node-id writing to the same object store; write-verification disabled in a store that drops object metadata (so AlreadyExists is not detected reliably); leftover WAL files from an older build at the next expected sequence number.","solutions":["Check for a second process using the same --node-id against the same object store and stop one of them.","Restart the affected node so it either picks up the new WAL position or fails cleanly; new writes will then flow to the healthy writer.","If the conflict is stale data from an older build, remove or archive the conflicting WAL file(s) at the conflicting path after confirming no live writer owns them.","Enable write verification (conditional puts) on your object store so duplicate writes are detected before this state is reached."],"exampleFix":"# before: two nodes, same node id\ninfluxdb3 serve --node-id node_a ...   # process 1\ninfluxdb3 serve --node-id node_a ...   # process 2 -> WalAlreadyWrittenTo\n# after: unique node ids per writer\ninfluxdb3 serve --node-id node_a ...\ninfluxdb3 serve --node-id node_b ...","handlingStrategy":"try-catch","validationCode":"# before starting a writer, verify no other process holds the node id\n# check running processes for the same --node-id and the same object-store prefix","typeGuard":"fn is_wal_ahead(err_msg: &str) -> bool { err_msg.contains(\"another process has written to the WAL ahead\") }","tryCatchPattern":"match wal.write_buffer(buffer, gen1).await {\n    Err(e) if e.to_string().contains(\"another process has written to the WAL ahead\") => {\n        // terminal: stop this writer; an operator must resolve the duplicate --node-id\n    }\n    other => { /* handle normally */ }\n}","preventionTips":["Guarantee unique --node-id per writer (orchestrator-enforced, e.g. StatefulSet ordinal).","Enable write verification / conditional puts on the object store.","After a crash, wait for/verify the old writer is dead before restarting with the same node id.","Alert on WriteResult::Error containing this message — it is a split-brain signal."],"tags":["rust","wal","object-store","concurrency","duplicate-writer"],"backgroundTag":"file-already-exists","analyzedSha":"06200ef96ba82c5f6727e5038a83af8e722c6875","analyzedAt":"2026-09-19T12:55:30.003Z","contentChangedAt":"2026-09-19T12:55:30.003Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}