[shun001]

Summary

This PR adds an opt-in NIXL payload backend for SimpleStorage. It introduces a common PayloadTransfer interface so the Manager and StorageUnit can use either ZMQ multipart messages or NIXL notifications with UCX READ for PUT, GET, and UPDATE. The design follows the interface proposed in [RFC #208](#208).

Design and implementation

• Common storage handling. The Manager submits a request header and ordered byte spans through PayloadTransfer. Both backends invoke the same StorageUnit handler for parsing, validation, reads, writes, and merges.
• Receiver-initiated transfers. The NIXL backend uses notifications to exchange request headers, buffer descriptors, and replies. For PUT and UPDATE, the Manager publishes the input buffer and the StorageUnit reads it before applying the operation. For GET, the StorageUnit publishes the encoded result and the Manager reads it.
• Buffer lifetime and write completion. The sender keeps its published buffer registered until it receives confirmation that the receiver has finished accessing it. PUT and UPDATE replies report storage acceptance separately from buffer release. If a write reply is lost, the Manager reports an unknown write outcome and avoids replaying the operation.
• Backend selection. ZMQ is the default payload backend and also serves administrative requests such as CLEAR and checkpoint operations. NIXL endpoints are distributed through the existing TQ bootstrap process.

To enable the NIXL backend:

backend:
  SimpleStorage:
    payload_transfer:
      backend: nixl-ucx

[chatgpt-codex-connector]

Codex Review Summary: ✅ Completed

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-11T07:12:10.015103Z	d394bf9	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: d394bf99bd

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[chatgpt-codex-connector]

Treat cancelled writes as outcome-unknown after sending

When a PUT/UPDATE task is cancelled after send_notification but before the reply, asyncio.CancelledError inherits BaseException and therefore bypasses this except Exception; the storage unit may still apply the write while the caller sees only cancellation. A caller using asyncio.wait_for and retrying can consequently apply a non-idempotent UPDATE twice, so this post-send cancellation path needs to finish determining the outcome or surface WriteOutcomeUnknown just like the timeout path.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Prevent oversized update acknowledgements after committing

When an UPDATE produces enough per-sample stored_shapes to make its reply exceed MAX_CONTROL_BYTES (1 MiB), _handle has already called apply_update before this packing attempt. _pack_control then falls into the outcome-unknown reply, so AsyncSimpleStorageManager.update_data raises before notify_data_update; for a newly added or shape-changing field, storage is committed while controller metadata remains stale. Large valid updates therefore deterministically leave the planes inconsistent; reject or preflight before applying, or carry the acknowledgement body outside the capped notification.

Useful? React with 👍 / 👎.

[ji-huazhong]

cc @Ginray