Adds AVEVA.Historian.Client.Redundancy — HistorianRedundantClient orchestrates
N single-historian members (IHistorianMember; default HistorianClientMember
over HistorianClient) as one logical client. Pure client-side, no server-side
redundancy protocol, no RE.
- Reads fail over to the next member in priority order. Streaming reads only
fail over BEFORE the first row is observed; a mid-stream failure propagates
(failing over mid-stream would risk duplicated/skipped rows).
- Writes fan out: WriteFanout AllMembers | PreferredOnly, with All | Any ack
policy, returning a per-member HistorianRedundantWriteResult.
- Per-member health: FailureThreshold demotes a failing member out of the
preferred pool; a background watchdog (PeriodicTimer) + CheckHealthAsync
re-probe and restore recovered members. GetStatus() snapshot + ActiveMember.
- Composes with R4.1: back a member's writes with a HistorianStoreForwardWriter
so a down member buffers and replays on recovery — the pragmatic client-side
equivalent of native ReSyncTags.
14 unit tests (no server): failover order, mid-stream no-failover, all-fail
aggregation, probe-any-up, fan-out ack policies, PreferredOnly, soft reject,
health demotion + CheckHealthAsync restore, watchdog recovery. Full suite 307
green. Roadmap R4.4 marked shipped.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC
Joseph Doherty