Streamed multipart uploads had two problems when the client uploaded parts
concurrently:
Parts arriving ahead of the next part needed by the backend stream were buffered
in memory without limit, acknowledging each part as soon as it was received. A
client uploading faster than the backend could drain would therefore balloon the
server's memory to the size of the upload. Buffering is now bounded a new
--multipart-streaming-buffer-limit flag (default 256Mi, 0 for unlimited): a part
that would take the buffer over the limit is not read until the stream drains,
applying backpressure to the client instead of using unbounded memory.
A part uploaded again with the same number - typically a client retrying after
its request timed out - left a stale copy in the reorder buffer which made
CompleteMultipartUpload fail with InvalidPart, aborting the whole upload.
Re-uploaded parts are now handled properly: a copy still in the buffer is
replaced, an identical copy of an already streamed part is accepted as a no-op,
and only replacing an already streamed part with different content (which the
in-order stream cannot honour) is rejected.
Nick Craig-Wood
b2d0642825