perf(historian): exact tag lookup and a non-thrashing presence cache (lmxopcua#746)

Every Gateway HistoryRead was preceded by a BrowseTagNames catalog stream keyed by a glob filter (a name with '*' or '?' streamed every match), and the 4096-entry presence cache evicted an arbitrary entry (Keys.First()) when full, so a sweep over more tags thrashed it. The presence check is now one exact unary GetTagMetadata (null = absent). Only the deployed gateway's known misparse of a missing tag (Internal / Unknown / InvalidDataException) falls back to the exact-name catalog check; any other failure propagates and never becomes absence. The positive TTL is 5 minutes (was 60 s); a full cache drops expired entries first, else the one closest to expiry. Wire tests cover the working, the misparsing and the refusing gateway. Rebased from the unpushed remed/lane-H2 branch (originally authored 2026-10-22 in session_01Ub9hGmYLQvn9XETzw7CMsT) onto current master. Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
2026-10-22 16:36:24 -04:00
parent 8dc594d8e4
commit bc7e58ed64
7 changed files with 187 additions and 19 deletions
@@ -82,16 +82,39 @@ public sealed class HistorianGatewayClientAdapter : IHistorianGatewayClient, IDi
    }

    /// <inheritdoc />
+    // One exact unary lookup (GetTagMetadata: null = absent). The deployed gateway's SDK misparses the reply for a MISSING
+    // tag and surfaces it as Internal ("GetTagInfo response ended unexpectedly"); only that answer falls back to the tag
+    // catalog, which proves presence by exact name (BrowseTagNames takes a glob, so a name holding '*' or '?' would stream
+    // every match — the exact compare keeps it correct). Any other failure propagates: it is never turned into absence.
    public async Task<bool> TagExistsAsync(string tag, CancellationToken ct)
    {
-        // older gateway SDKs misparse a missing GetTagInfo response as Internal. A catalog query proves
-        // absence without guessing from an error. Even a glob-like tag is checked by exact name, never by row count.
+        try
+        {
+            return await _inner.GetTagMetadataAsync(tag, ct).ConfigureAwait(false) is not null;
+        }
+        catch (Exception ex) when (!ct.IsCancellationRequested && IsMetadataMisparse(ex))
+        {
+            // Fall through to the catalog.
+        }
+
        var found = false;
        await foreach (var name in _inner.BrowseTagNamesAsync(tag, ct).ConfigureAwait(false))
            found |= string.Equals(name, tag, StringComparison.OrdinalIgnoreCase);
        return found; // drain first: a trailing stream fault must propagate and must not become a cache entry
    }

+    /// <summary>The known metadata misparse: an Internal/Unknown status, or the parser's own InvalidDataException.</summary>
+    private static bool IsMetadataMisparse(Exception ex)
+    {
+        for (Exception? e = ex; e is not null; e = e.InnerException)
+        {
+            if (e is System.IO.InvalidDataException) return true;
+            if (e is Grpc.Core.RpcException rpc)
+                return rpc.StatusCode is Grpc.Core.StatusCode.Internal or Grpc.Core.StatusCode.Unknown;
+        }
+        return false;
+    }
+
    /// <inheritdoc />
    public IAsyncEnumerable<HistorianSample> ReadRawAsync(
        string tag, DateTime startUtc, DateTime endUtc, int maxValues, CancellationToken ct) =>