perf: add 8 MiB buffered reader to S3 upload pipe#216
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joshfriend merged 1 commit intomainfrom Mar 23, 2026
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The save path streams tar|zstd output through an io.Pipe into the multipart uploader. The pipe has zero internal buffer — when all upload workers are busy sending parts to S3, the reader goroutine blocks, which blocks the pipe, which stalls the archive process. Adding an 8 MiB bufio wrapper lets the archive keep producing data while workers are busy, smoothing out the stalls. Benchmarked on r8id.metal-48xlarge with a 2.4 GB compressed cache bundle.
alecthomas
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Mar 23, 2026
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The save path streams tar|zstd output through an io.Pipe into the multipart uploader. The pipe has zero internal buffer — when all upload workers are busy sending parts to S3, the reader goroutine blocks, which blocks the pipe, which stalls the archive process.
Adding an 8 MiB
bufiowrapper lets the archive keep producing data while workers are busy, smoothing out the stalls. Benchmarked on r8id.metal-48xlarge with a 2.4 GB compressed cache bundle.