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fix(historian): #692 review — a drained tie cluster never resumes onto the exclusive EndTime

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F1 (pre-existing): SliceTieCluster continued a forward read while next <= endUtc, but the
forward window is end-exclusive; an oversized cluster one step below EndTime resumed AT
EndTime, the resume became a start == end point read and returned the EndTime samples as
data (microsecond: EndTime 8.1 us truncated to 8.0). Continue only while next is strictly
before EndTime truncated to the backend resolution.

Tests: A_tie_cluster_just_below_the_end_time_never_resumes_onto_the_end_time (native +
microsecond; both fail on the old rule) and
A_cursor_inside_a_tie_cluster_over_fetches_without_a_normal_read_first (pins the
WithinTieCluster shortcut by per-page read count; fails with the shortcut disabled).
Docs: the oversized-cluster exception to 'every page full / no lookahead => last' (F2),
and the N + skip + 1 strict-ceiling edge note referencing #694 (F4).
This commit is contained in:
Joseph Doherty
2026-10-13 01:02:12 -04:00
parent 3d7eea6280
commit e04e1bf127
3 changed files with 83 additions and 11 deletions
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src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/HistoryPaging.cs
+8 -7
View File
@@ -258,12 +258,11 @@ internal static class HistoryPaging
/// <param name="cap">The client's per-page cap (<c>NumValuesPerNode</c>); must be &gt; 0 to make progress.</param>
/// <param name="boundaryT">The single SourceTimestamp every tie in the cluster shares.</param>
/// <param name="endUtc">The (inclusive) upper bound of the read window; unchanged across pages.
/// OpcUaServer-003, accepted by design: the backend contract
/// (<c>IHistorianDataSource.ReadRawAsync</c>) treats <c>endUtc</c> as EXCLUSIVE, so the
/// <c>next &lt;= endUtc</c> test here is deliberately the conservative side — at worst one extra
/// empty resume page (<c>[endUtc, endUtc)</c> → GoodNoData, no continuation point), never a
/// dropped or duplicated sample. Tightening to <c>&lt;</c> would be correct only if the live
/// backend's boundary is confirmed exclusive; it is not worth the opposite off-by-one risk.</param>
/// The forward window is end-EXCLUSIVE (Part 11; the <c>IHistorianDataSource.ReadRawAsync</c> contract), so a drained
/// cluster continues only while <c>next</c> is strictly before <paramref name="endUtc"/> truncated to
/// <paramref name="resolutionTicks"/>. (OpcUaServer-003 had kept <c>next &lt;= endUtc</c> as "the conservative side",
/// but it was not: resuming AT EndTime makes the next read a <c>start == end</c> point read, which returns the samples
/// at EndTime as data — #692 review F1; on a microsecond backend EndTime is truncated first.)</param>
/// <param name="sliceStart">The index into the cluster the emitted slice starts at (clamped to the count).</param>
/// <param name="sliceCount">How many ties the emitted slice contains (may be <c>0</c> on a stale-skip self-heal).</param>
/// <param name="nextStartUtc">The next page's inclusive start: <paramref name="boundaryT"/> while the
@@ -306,7 +305,9 @@ internal static class HistoryPaging
else
{
var next = boundaryT.AddTicks(resolutionTicks);
if (next <= endUtc) { nextStartUtc = next; nextSkip = 0; }
// The forward window is end-EXCLUSIVE, at the backend's resolution: resuming AT EndTime would turn the next read
// into a start == end point read, which returns the samples at EndTime as data (#692 review F1).
if (next.Ticks < endUtc.Ticks - endUtc.Ticks % resolutionTicks) { nextStartUtc = next; nextSkip = 0; }
else { nextStartUtc = null; nextSkip = 0; }
}
}