docs(historian): #691.1 Gateway start-bound lookup inherits the per-millisecond tie limit

2026-10-12 18:20:14 -04:00
parent 942ca7bc14
commit 15ccd9b722
1 changed files with 3 additions and 0 deletions
@@ -804,6 +804,9 @@ switch `ServerHistorian:HonorReturnBounds = false` restores the pre-#691 behavio
  the microsecond, "on the bound" compares at that resolution, so a sample at ⌊StartTime⌋ is never returned twice. A first page
  therefore costs up to three backend reads (start bound, data, end bound). The `BoundingValueConformance` suite pins those exact
  lookup reads on SqlServer and QuestDB.
+  ⚠️ On the **Gateway** the start-bound walk-back is subject to the #689 per-millisecond tie limit: if the millisecond holding the
+  bound has more than `MaxTieClusterOverfetch` samples, the lookup cannot pick the cluster's last sample without reading it all, so
+  the **whole node** read fails `BadTooManyOperations` (even though the data read alone would succeed) rather than return a wrong bound.
 - **Modified reads:** `IsReadModified = true` with `ReturnBounds = true` is `Bad_InvalidArgument` per node (Part 11 §6.5.3.3).
 - **Kill switch:** `ServerHistorian:HonorReturnBounds` (default `true`). `false` ignores `ReturnBounds` exactly as before #691 —
  stored samples only, and no modified-read rejection.