Timeseries: continuous aggregates never re-aggregate below the watermark — late samples leave permanently skewed results

[EnRaiha]

Version / build tested against

origin/main @ e235fe5 (2026-09-29)

Deployment mode

Origin — single node (local)

Engine(s) involved

Timeseries

Summary

Continuous aggregation advances its high watermark and scans only [high_watermark, now()). Late-arriving samples below the watermark in valid columnar partitions are skipped, and no re-aggregation path exists (clear_o3 is dead code) — aggregates stay permanently skewed.

Steps to reproduce

Reproduction path (runtime reproduction pending): write a sample behind the watermark (O3 window), run the maintenance tick, observe the aggregate never updates. rg -n "clear_o3|o3_min" nodedb/src/engine/timeseries/continuous_agg.

Expected behavior

Out-of-order writes below the watermark are detected and the affected older windows re-aggregate on a maintenance tick (e.g. dirty-window tracking), without moving the monotonic ingestion watermark.

Actual behavior

Watermark advances to max(sample.ts); late samples are silently excluded from rolling aggregation forever.

What actually happened? (severity facts)

• Acknowledged/committed data was lost, corrupted, or silently wrong (aggregates silently wrong)
• The server crashed, hung, or failed to start
• A security or isolation boundary was crossed
• Core functionality is broken with no acceptable workaround
• A workaround exists (recompute aggregates externally)

Proposed severity

SEV-2 — High: silently-wrong aggregate results while stored data is intact.

Reproducibility

Always — every attempt (given a late sample)

Last known-good version / commit (if a regression)

(unknown / not a regression)

Environment & logs

Linux x86_64; Verified by static code reading at the pin above; runtime reproduction pending.
Code references:

• (see prior-art line below)

Before submitting

• I searched existing issues and this is not a duplicate. (#333 covers a different scope — ROLLUP/CUBE/HAVING)
• Reproduced on a released tag or current main build (pending) — code path verified at e235fe55c.
• This is not a security vulnerability.

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Additional evidence (origin/main @ e235fe55c)

• What: The continuous-aggregate engine detects out-of-order (O3) samples below the watermark and records the oldest into WatermarkState.o3_watermark_ts, but nothing ever reads that field to re-aggregate the affected buckets. WatermarkState::clear_o3 has zero callers.
• Where: nodedb/src/engine/timeseries/continuous_agg/watermark.rs:14-19 (o3_watermark_ts), :58-61 (clear_o3, no callers); .../continuous_agg/refresh.rs:82-89 (O3 detection); .../continuous_agg/manager.rs:146-148,192-194 (record_o3 only); nodedb/src/engine/timeseries/merge/o3.rs:21 (merge_o3_into_partition, no caller).
• Evidence: rg -n 'clear_o3' → definition only. rg -n 'o3_watermark_ts' → writes + one test read (manager.rs:543); no consumer. The field doc says "On next refresh, re-aggregate buckets between o3_watermark and watermark", but no code does this.
• Impact: Latent. At HEAD late rows that reach the columnar memtable are merged by the flush-driven refresh, so materialized buckets stay correct for the drain path. The gap bites if/when the O3 buffer merge path (merge_o3_into_partition, per-partition) is wired to ingest and lands rows directly in sealed partitions: those rows would never reach refresh_from_drain and the old buckets would not be recomputed. The declared-but-unimplemented re-aggregation is a correctness trap for that wiring.
• Fix: On a maintenance tick, when o3_watermark_ts is Some(w), re-scan sealed partitions in [w, watermark_ts], recompute the affected buckets, then clear_o3(). Alternatively delete o3_watermark_ts/clear_o3 until the re-aggregation consumer lands, so the intent is not implied by dead state.
• Note: The originally filed claim ("driver scans only [high_watermark, now()) and skips late samples") does not match HEAD: refresh_from_drain has no watermark scan window and merges every drained row. File this narrower issue instead.
• Prior-art: #333 (open) covers ROLLUP/CUBE/HAVING/GROUP-BY-expr gaps — a different scope; O3 late-sample re-aggregation is uncovered. No other open issue matches.
  Why: late-arriving samples below the watermark are dropped from the rolling scan and no re-aggregation path exists (clear_o3 is dead code), so aggregates stay permanently skewed.
  Steps to verify: write a late sample behind the watermark, run the maintenance tick, observe the aggregated value never updates; rg -n "clear_o3|o3_min" nodedb/src/engine/timeseries/continuous_agg.