{"record":{"id":"fc1c8bb8248824bb","repo":"nats-io/nats-server","slug":"failed-to-compress-block-w","errorCode":null,"errorMessage":"failed to compress block: %w","messagePattern":"failed to compress block: %w","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"server/filestore.go","lineNumber":8041,"sourceCode":"\tif err != nil {\n\t\treturn fmt.Errorf(\"failed to create temporary file: %w\", err)\n\t}\n\n\terrorCleanup := func(err error) error {\n\t\t_ = tmpFD.Close()\n\t\t_ = os.Remove(tmpFN)\n\t\treturn err\n\t}\n\n\talg := NoCompression\n\tif calg := mb.fs.fcfg.Compression; calg != NoCompression && allowCompress {\n\t\talg = calg\n\t\t// The original buffer at this point is uncompressed, so we will now compress\n\t\t// it if needed. Note that if the selected algorithm is NoCompression, the\n\t\t// Compress function will just return the input buffer unmodified.\n\t\toriginalSize := len(buf)\n\t\tif buf, err = alg.Compress(buf); err != nil {\n\t\t\treturn errorCleanup(fmt.Errorf(\"failed to compress block: %w\", err))\n\t\t}\n\n\t\t// We only need to write out the metadata header if compression is enabled.\n\t\t// If we're trying to uncompress the file on disk at this point, don't bother\n\t\t// writing metadata.\n\t\tmeta := &CompressionInfo{\n\t\t\tAlgorithm:    alg,\n\t\t\tOriginalSize: uint64(originalSize),\n\t\t}\n\t\tbuf = append(meta.MarshalMetadata(), buf...)\n\t}\n\n\t// Re-encrypt the block if necessary.\n\tif err = mb.encryptOrDecryptIfNeeded(buf); err != nil {\n\t\treturn errorCleanup(err)\n\t}\n\n\t// Write the new block data (which might be compressed or encrypted) to the","sourceCodeStart":8023,"sourceCodeEnd":8059,"githubUrl":"https://github.com/nats-io/nats-server/blob/3a66a489d262bf89b71a71c955c94920394532f3/server/filestore.go#L8023-L8059","documentation":"This error is returned when writing a message block to disk in NATS JetStream's file-based message store. During block update, the message buffer is compressed with the algorithm selected for the block (e.g. s2); if alg.Compress(buf) fails, the update is aborted with this wrapped error and the temporary file is cleaned up. It indicates a failure in the compression layer, not in message delivery itself.","triggerScenarios":"Calling stream/msg-store APIs that rewrite or update an existing message block (e.g. updating a message in a stream with compression enabled) when the compressor's Compress() call returns an error on the block buffer.","commonSituations":"Compressed stream files (file store with compression configured), corrupted or out-of-memory conditions during buffer allocation inside the compression library, or oversized/malformed block buffers in low-memory environments.","solutions":["Check available memory; compression allocates output buffers and can fail under memory pressure.","Retry the operation; if the error is transient, the block temp file is cleaned up so the original block remains intact.","If persistent, disable stream compression or move the stream to a host with more resources.","Report/check for compression library (s2/snappy) issues on the NATS version in use; upgrade NATS Server."],"exampleFix":"// before: stream config with compression\nCompression: nats.FileCompressS2\n// after: temporarily disable compression to isolate the failure\nCompression: nats.NoCompression","handlingStrategy":"retry","validationCode":null,"typeGuard":null,"tryCatchPattern":"// retry with backoff; compression failure aborts update but leaves original block intact\nfor i := 0; i < 3; i++ {\n    if err := updateOp(); err == nil { break }\n    time.Sleep(time.Duration(1<<i) * 100 * time.Millisecond)\n}","preventionTips":["Provision adequate memory for the server; compression allocates buffers.","Monitor memory usage and set appropriate server limits.","Keep NATS Server updated for compression library fixes.","Test streams with compression enabled before production rollout."],"tags":["filestore","compression","jetstream","go"],"backgroundTag":"block-compression-failed","analyzedSha":"3a66a489d262bf89b71a71c955c94920394532f3","analyzedAt":"2026-09-02T04:41:54.247Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}