Merge feat/675-reverse-event-paging: reverse event HistoryRead paging, end-only backward, Gateway MaxValue pin (#675)

2026-10-11 11:23:51 -04:00
parent e59ab69398 8d154c6a81
commit 8e6ac4b344
20 changed files with 752 additions and 60 deletions
@@ -320,8 +320,18 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
    ///     of <c>"{EventTimeUtc.Ticks}|{EventId}"</c> of that first not-returned event (opaque to callers; only
    ///     its presence is contractual).
    /// </remarks>
+    public Task<HistoricalEventsResult> ReadEventsAsync(
+        string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken cancellationToken) =>
+        ReadEventsAsync(sourceName, startUtc, endUtc, maxEvents, reverse: false, cancellationToken);
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     Forward is the five-argument read. Reverse (Gitea #675) is <c>(lo, hi]</c> ordered by
+    ///     <c>(EventTimeUtc, EventId)</c> DESCENDING — the clustered index scanned backwards — so <c>TOP</c> keeps the latest
+    ///     events; truncation and the continuation point work as forward.
+    /// </remarks>
    public async Task<HistoricalEventsResult> ReadEventsAsync(
-        string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, CancellationToken cancellationToken)
+        string? sourceName, DateTime startUtc, DateTime endUtc, int maxEvents, bool reverse, CancellationToken cancellationToken)
    {
        // No stored event can carry a source longer than the column (the alarm writer dead-letters it rather than
        // truncating), so an over-long filter matches nothing — never a truncated prefix of someone else's source.
@@ -334,9 +344,10 @@ public sealed class SqlServerHistorianDataSource : IHistorianDataSource
            var bounded = maxEvents > 0 && maxEvents < int.MaxValue;
            var sql =
                $"SELECT {(bounded ? "TOP (@take) " : "")}EventId, SourceName, EventTimeUtc, ReceivedTimeUtc, Message, Severity " +
-                $"FROM {_conn.Q("Event")} WHERE EventTimeUtc >= @lo AND EventTimeUtc < @hi" +
+                $"FROM {_conn.Q("Event")} WHERE " +
+                (reverse ? "EventTimeUtc > @lo AND EventTimeUtc <= @hi" : "EventTimeUtc >= @lo AND EventTimeUtc < @hi") +
                (sourceName is null ? "" : " AND SourceName = @source") +
-                " ORDER BY EventTimeUtc ASC, EventId ASC";
+                (reverse ? " ORDER BY EventTimeUtc DESC, EventId DESC" : " ORDER BY EventTimeUtc ASC, EventId ASC");

            await using var conn = await _conn.OpenAsync(cancellationToken).ConfigureAwait(false);
            await using var cmd = _conn.CreateCommand(conn, sql);