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fix(alarms): truncation-safe transitions; perf: single-pass alarm parse; configurable poll cadence

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Joseph Doherty
2026-08-15 17:04:06 -04:00
parent 94fdc18c3c
commit f3e1de5f37
10 changed files with 910 additions and 33 deletions
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docs/GatewayConfiguration.md
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@@ -417,6 +417,8 @@ behavior.
| `MxGateway:Alarms:SubscriptionExpression` | _(empty)_ | AVEVA alarm-subscription expression the monitor subscribes on startup, in canonical `\\<machine>\Galaxy!<area>` form. The literal `Galaxy` provider is correct regardless of the Galaxy database name. When empty and `Enabled` is `true`, the gateway falls back to `\\<MachineName>\Galaxy!<DefaultArea>` if `DefaultArea` is set. |
| `MxGateway:Alarms:DefaultArea` | _(empty)_ | Area name used to compose a default subscription when `SubscriptionExpression` is empty. If both are empty while `Enabled` is `true`, the monitor faults with a configuration diagnostic. |
| `MxGateway:Alarms:ReconcileIntervalSeconds` | `30` | How often the monitor reconciles its in-process alarm cache against the worker's authoritative active-alarm snapshot, catching transitions the live poll-and-diff feed missed. Floored at 5 seconds. |
| `MxGateway:Alarms:PollIntervalMilliseconds` | `500` | Cadence at which the worker's STA polls the AVEVA alarm consumer (`GetXmlCurrentAlarms2`) for the active-alarm snapshot the live feed diffs. Must be `>= 100`: every poll is a COM call plus an XML parse on the same STA that serves reads and writes, so a tighter cadence starves the command path. The gateway conveys the value to the worker via the `MXGATEWAY_ALARM_POLL_INTERVAL_MS` environment variable; a missing or unusable value leaves the worker on the 500 ms default rather than failing the session. |
| `MxGateway:Alarms:MaxAlarmsPerFetch` | `1024` | Cap the worker passes to `GetXmlCurrentAlarms2`'s `maxAlmCnt`. Must be `>= 64`. It doubles as the **truncation threshold**: a fetch returning exactly this many records is treated as truncated, because the COM API caps its reply with no "more available" flag. On a truncated poll the worker retains the alarms the capped reply could not mention instead of letting their absence read as a clear, and logs a rate-limited `AlarmSnapshotTruncated` warning (identifiers and counts only). Raise this on galaxies whose steady-state active-alarm count approaches the cap — a galaxy permanently above it holds stale entries in the snapshot until a sub-cap poll. Conveyed to the worker via the `MXGATEWAY_ALARM_MAX_ALARMS_PER_FETCH` environment variable; a missing or unusable value leaves the worker on the 1024 default. |
The alarm monitor is independent of client sessions: `AcknowledgeAlarm` and
`StreamAlarms` are session-less RPCs served by the monitor.