[feat] PIP-473: Metadata-Driven Transactions for Scalable Topics#25693
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merlimat merged 3 commits intoMay 12, 2026
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Sub-PIP of PIP-460 (Scalable Topics). Defines transactional support for scalable topics by replacing the in-stream commit/abort marker model with metadata-store-backed state. Adds parallel implementations of TransactionBuffer, PendingAckStore, and Transaction Coordinator that write nothing to any data stream, so sealed segments (split/merge) no longer strand in-flight transactions. Reuses dispatcher, client API, and TC wire commands; legacy in-stream-marker components remain unchanged for persistent:// topics.
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Co-authored-by: Lari Hotari <lhotari@users.noreply.github.com>
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LGTM. Please check the review comments and mark them resolved.
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Summary
Sub-PIP of PIP-460: Scalable Topics.
Proposes a transaction model for scalable topics that replaces the in-stream commit/abort marker mechanism with metadata-store-backed state, so transactions compose correctly with the segment lifecycle (splits, merges, sealed segments).
The shape of the change:
MetadataTransactionBuffer— newTransactionBufferimplementation forsegment://topics. Writes nothing to the topic's data stream; transactional state lives as records and secondary indexes in the metadata store.MetadataPendingAckStore— newPendingAckStoreimplementation forsegment://subscriptions. No sibling pending-ack topic.MetadataStoreextensions — surface partition-key co-location, sequential keys, and secondary indexes with range-watch. Default backend (Oxia) maps to native primitives; ZooKeeper and others can implement them sub-optimally without affecting correctness.Existing
persistent://topic behavior is unchanged. v4 transactions keep their current implementation byte-for-byte.The PIP is self-contained — full data model, end-to-end flows (publish, end-txn, dispatch, recovery, GC), backward-compat, and rejected alternatives are in the document.
Test plan