User-reported: the integration tests leave instances behind and take 18+ GB.
Measured before changing anything — a SINGLE Host.IntegrationTests process peaked
at 30,153 MB RSS across its ~200 tests.
The cause was not a leak and not parallelism. Referencing the Host drags in the
ASP.NET Core framework reference, which turns Server GC on by default: one heap
per core, tuned for throughput and deliberately reluctant to hand memory back.
Correct for a server, wrong for a test host. Workstation GC takes the same suite
from 30,153 MB to 6,717 MB — 78% less — with no change in runtime (45s).
Two hypotheses were measured and rejected on the way, recorded here so nobody
re-runs the experiment: capping xunit maxParallelThreads to 4 cost 29% wall-clock
and saved nothing (30,153 -> 31,115 MB, i.e. noise), and it turns out a single
process was doing all of it. Reverted.
The harness fix is real but was worth only 4% on its own: TwoNodeClusterHarness
disposed each node without stopping it first, and IHost.DisposeAsync only disposes
the service provider — it never invokes IHostedService.StopAsync, which is where
Akka.Hosting terminates the ActorSystem. So every test left two live ActorSystems,
remoting transports and dispatcher pools included, rooted for the process
lifetime. The class doc-comment asserted the opposite ("DisposeAsync, which runs
CoordinatedShutdown"); it was wrong, and StopNodeBAsync inherited the same bug on
a path failover tests depend on.
The payoff is larger than the memory number. Two failures I had classified as
known-flaky baseline noise now pass consistently:
RoslynVirtualTagEvaluatorTests.Evaluate_racing_ClearCompiledScripts_never_fails_with_disposed
and ContinuousHistorizationRecorderTests.Retry_after_writer_failure_eventually_acks.
They were never flaky — they were starved. Full solution: peak summed test-process
RSS 15.2 GB, zero new failures, two fewer.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Joseph Doherty
835fc08c3f