docs(cayenne): datalake promotion is incremental carry-forward, not whole-table

[claudespice]

Summary

The Cayenne Cold Object-Store Tier "How it works" section described promotion as re-materializing the whole visible table each cycle. spiceai/spiceai#11745 (merged, on trunk as 6e0751ae8) rewrote datalake (cold) tier promotion to incremental carry-forward, so the published description is now stale.

Corrected against current trunk source (crates/cayenne/src/provider/cold_partition.rs, pk_index.rs):

• Promotion (write path) — now incremental carry-forward: the cold manifest is classified into dirty files (may host a tombstoned key — detected via per-PK-column min/max rectangles from persisted stats, refined by a per-file PK bloom, conservative in the safe direction) and clean files carried forward by manifest reference and never re-read. Only the warm delta plus dirty files are re-read, Z-order clustered, and written under a per-promotion prefix — so cost tracks changed data, not table size.
• Cross-tier scan (read path) — added that each cold file's PK bloom lets an upsert keyset rebuild answer cold-tier key existence without an object-store scan.
• Physical GC — new bullet: periodic manifest-rooted mark-and-sweep reclaims objects orphaned by carry-forward rewrites, every cayenne_datalake_gc_interval_ms (default 5m), which doubles as the orphan grace period.

Datalake/cold-tier is vNext-only (params exist only under website/docs/, not versioned_docs/), so no versioned propagation is needed. Prose-only diff — no new links or tags.

Source PRs

• feat(cayenne): incremental datalake promotion, per-file PK blooms, physical GC spiceai#11745 — feat(cayenne): incremental datalake promotion, per-file PK blooms, physical GC

Test plan

• cd website && npm run build passes (Docusaurus; Generated static files, exit 0)
• Versioned-docs propagation checked — vNext-only feature, no versioned copies exist
• Files updated: 1 (website/docs/components/data-accelerators/cayenne/index.md)

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