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perf: add 8 MiB buffered reader to S3 upload pipe #216

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Merged
joshfriend merged 1 commit into from
Mar 23, 2026
Merged

perf: add 8 MiB buffered reader to S3 upload pipe #216

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15 changes: 11 additions & 4 deletions internal/cache/s3.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package cache

import (
"bufio"
"context"
"crypto/tls"
"encoding/json"
Expand Down Expand Up @@ -350,8 +351,14 @@ func (s *S3) Create(ctx context.Context, key Key, headers http.Header, ttl time.
errCh: make(chan error, 1),
}

// Start upload in background goroutine
go writer.upload(pr)
// Start upload in background goroutine. The buffered reader decouples the
// upstream pipe (zero-buffer io.Pipe from the archive process) from the
// upload chunking loop. Without it, when the uploader blocks on a full
// jobs channel or slow S3 part upload, the archive goroutine stalls
// because nobody is consuming the pipe. The 8 MiB buffer absorbs ongoing
// archive output during those brief stalls.
br := bufio.NewReaderSize(pr, 8<<20)
go writer.upload(pr, br)

return writer, nil
}
Expand Down Expand Up @@ -422,7 +429,7 @@ func (w *s3Writer) Close() error {
return nil
}

func (w *s3Writer) upload(pr *io.PipeReader) {
func (w *s3Writer) upload(pr *io.PipeReader, r io.Reader) {
var uploadErr error
defer func() {
// Use CloseWithError to propagate any error to the writer side
Expand Down Expand Up @@ -471,7 +478,7 @@ func (w *s3Writer) upload(pr *io.PipeReader) {
w.ctx,
w.s3.config.Bucket,
objectName,
pr,
r,
-1,
opts,
)
Expand Down