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fix(historian): #694 page raw reads at a strict gateway's learned ceiling; opt-in EventReadHorizon

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Item 1: IHistorianDataSource.MaxRawValuesPerRead (Gateway: learned ceiling - 16 = L; 0 elsewhere, guard-tested).
RawPageLimit plans every raw page on top of #692's lookahead: with L > 0 the read (page P + boundary ties k
+ lookahead) is <= L, P = min(N, L - k - 1) (uncapped: L - k - 1); no room => straight to the tie-cluster
over-fetch (never an uncapped or underflowing request). One re-plan + re-read when the read taught a new
limit or was refused for crowding pre-window rows (HistoryReadLimitExceededException.PreWindowRows): the
page shrinks by them. Over-fetch bound min(MaxTieClusterOverfetch, L - 1); slice size never 0.
Review fixes: F1 a window starting at/before the epoch counts AVEVA's synthetic row as pre-window (a
ceiling-truncated read was reported complete); F2 the page path disables ReverseRawReader's own re-run
(cold end-only ceiling 20/N=3000 cost 3,023 reads, now <= 40); F3 crowded look-back re-read around, not
refused; F4 the #687 crowding re-read room at least doubles (up to 8 re-reads), so a cluster of hundreds
just before a resume point no longer fails on a default gateway; a crowding refusal that leaves no room
is BadTooManyOperations, never a tick-by-tick cursor.

Item 2: ServerHistorian:EventReadHorizon (default 00:00:00 = exact, unchanged). When set, every fresh
HistoryReadEvents window's earlier bound is raised to now - horizon (both directions, all backends).
Lossy by design; documented.

Item 3 (native TimeAverage/Total re-check) stays blocked on historiangw#27.
This commit is contained in:
Joseph Doherty
2026-10-13 00:52:12 -04:00
parent a5a0496176
commit 3c3513ea3e
23 changed files with 1461 additions and 79 deletions
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src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.SqlServer/SqlServerHistorianDataSource.cs
+4
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@@ -316,6 +316,10 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
/// <remarks>Reverse raw reads are served natively (<c>(end, start]</c>, <c>ORDER BY … DESC</c>; #669/#686).</remarks>
public bool SupportsReverseRaw => true;
/// <inheritdoc />
/// <remarks><c>0</c>: a capped raw read is one bounded statement — no backend row ceiling (Gitea #694).</remarks>
public int MaxRawValuesPerRead => 0;
/// <inheritdoc />
/// <remarks>Reverse events reads are served natively (<c>ORDER BY … DESC</c>, Gitea #675).</remarks>
public bool SupportsReverseEvents => true;