The WP-4 runs measured the stream path only up to the bounded send channel;
the probe deliberately substituted the socket hop with a controllable reader,
which is exactly where the R2 SiteStreamEventBatcher lives — so batching had
never been in any benchmark's hot path. The harness now also attaches per-site
wire probes: a real Kestrel h2c listener hosting the production
SiteStreamGrpcServer, dialed by the production SiteStreamGrpcClient with
batching negotiated, batch sizes read from the production batch_size histogram
via a MeterListener (--wire-probes-per-site, default 10; 0 restores the old
shape). Full-scale run (10x500x75, 20-min window, results doc §8 + raw JSON):
899,807 events in 12,462 frames (mean 72.2 ev/frame, p50=p99=75), wire P99
43.4 ms vs the 250 ms budget — every batch pays the full 25 ms linger since a
75-event burst never hits the 100 cap — zero drops, zero faults, offered load
100.0% of nominal with fan-out doubled. CI smoke Fact now asserts the wire
path carries traffic and observes frames.
Standalone console harness under tests/ZB.MOM.WW.ScadaBridge.LoadHarness plus a
scaled-down Category=Performance smoke [Fact] in PerformanceTests. Deliberately an
Exe rather than an xunit suite: the Performance trait enables a filter but does not
exclude by default, so a 20-minute test would run on every 'dotnet test' of the slnx.
What is real: per-site ActorSystem + LocalDb SQLite file, the real DCL
(DataConnectionManagerActor/DataConnectionActor over a SimulatedDataConnection
registered through the documented DataConnectionFactory.RegisterAdapter seam), real
InstanceActors fed real TagValueUpdates, the real SiteStreamManager, real
StreamRelayActor + production-capacity bounded DropOldest channel, real
StoreAndForwardService/Storage, real SiteHealthCollector + CentralHealthAggregator.
Only the socket hops are stood in for.
Measures: end-to-end tag update latency (the emit instant rides
TagValueUpdate.Timestamp verbatim to the subscriber), instance ramp, memory
growth/CPU over a steady-state window, health report and debug view latency under
load, S&F concurrent buffering + drain throughput, and slow-subscriber isolation.
Joseph Doherty