storage/blob/s3: Force a smaller PartSize when blob size is unknown

Blob size would be unknown ahead of time if message store compression is used (e.g. in imapsql).

Part of #395 fix

internal/storage/blob/s3/s3.go

@@ -116,7 +116,16 @@ func (s *Store) Create(ctx context.Context, key string, blobSize int64) (module.
  errCh := make(chan error, 1)
 
  go func() {
- _, err := s.cl.PutObject(ctx, s.bucketName, s.objectPrefix+key, pr, blobSize, minio.PutObjectOptions{})
+ partSize := uint64(0)
+ if blobSize == module.UnknownBlobSize {
+ // Without this, minio-go will allocate 500 MiB buffer which
+ // is a little too much.
+ // https://github.com/minio/minio-go/issues/1478
+ partSize = 1 * 1024 * 1024 /* 1 MiB */
+ }
+ _, err := s.cl.PutObject(ctx, s.bucketName, s.objectPrefix+key, pr, blobSize, minio.PutObjectOptions{
+ PartSize: partSize,
+ })
  if err != nil {
  pr.CloseWithError(fmt.Errorf("s3 PutObject: %w", err))
  }