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fix(historian): #691.2 serve reverse native TimeAverage/Total on Gateway via forward reads on the later-anchored #677 grid

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Joseph Doherty
2026-10-12 16:17:05 -04:00
parent dbffb6bdb4
commit 0e47e887de
7 changed files with 349 additions and 6 deletions
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docs/Historian.md
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@@ -880,8 +880,19 @@ fixed:
`HistorianTagDefinition.IntegralDivisor` is `0`, so `GatewayTagProvisioner` now sends **`IntegralDivisor = 1`** explicitly on every
`EnsureTags` — the value·seconds unit the SQL backends' `Total` uses. A tag provisioned earlier keeps its divisor until its next
`EnsureTags` (an upsert). The live magnitude check against AVEVA (a constant 1 integrated over 1 s reads 1) passed on 2026-10-12 at the AVEVA
level; end to end it waits on historiangw#27 (above). Reverse processed reads of the AVEVA-native `TimeAverage`/`Total` are not re-anchored by #677 (the gateway refuses `end < start`);
the raw-evaluated per-sample aggregates (#681) do follow #677. Since #681 every native bucket is stamped with its interval **start**
level; end to end it waits on historiangw#27 (above). ⚠️ **Reverse native reads (#691.2, client-visible).** A reverse processed read (`StartTime > EndTime`) of the AVEVA-native
`TimeAverage`/`Total` used to reach the gateway as `start > end` and fail the node (`InvalidArgument`, counted as a backend failure). It
now follows #677 like the SQL backends and the raw-evaluated per-sample aggregates (#681): window `(EndTime, StartTime]`, intervals
stepping back from `StartTime`, the clipped interval the **earliest**, each stamped with its **later** edge, newest first. It is served
by **forward** native requests on that later-anchored grid (`NativeReverseAggregatePlan` — AVEVA anchors a native read's grid at the
request start): one read `[O + I·f, StartTime)` with the interval `I` for the whole intervals (`O = StartTime − n·I`), and — when the
window is not a whole number of intervals — a second read over exactly the clipped earliest span `[EndTime, O + I)` with its own width
as the interval, so AVEVA never averages time before the window. A time-weighted value over `[a, b)` and over `(a, b]` is the same
integral (two instants apart), so each forward row is the reverse interval's value; rows are mapped exactly as forward native rows
(#685) and the clipped interval carries the **Partial** bit unless Bad (Part 13 §5.3.3.2 Case 3, as on the SQL backends — the forward
native read still sets no Partial bit). An interval AVEVA answers no row for is absent, as on a forward native read. ⚠️ Pinned against
a native-mode fake only: under historiangw#27 AVEVA answers one row per request today, so end to end a reverse native read is as wrong
as a forward one until the gateway is fixed — re-run the reverse leg then. Since #681 every native bucket is stamped with its interval **start**
(Part 13; it was the interval end) and carries the Calculated info bits (`Good` ⇒ `0x00000401`, no data ⇒ `BadNoData | 0x401`).
The live AVEVA gate (2026-10-12) confirmed `start_time` is the interval start (and the `value·s` unit). Previously noted as
pending: it reads the aggregate row's `start_time`, which histsdk decodes from a row