Fix #420: cap concurrent projection rebuilds per database - #425
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Adds a `--max-concurrent` flag to the `projections rebuild` CLI and applies it as the MaxDegreeOfParallelism of the per-database rebuild fan-out in ProjectionHost.TryRebuildShardsAsync. Previously the fan-out over projections was unbounded, so a wide store (many projections, especially under per-tenant event partitioning) could spawn enough concurrent rebuild agents to blow the connection pool and thrash the buffer cache. A null / non-positive flag preserves the historical unbounded behavior, and the effective cap is logged at rebuild start so operators can confirm the throttle. ProjectionInput.ResolveMaxDegreeOfParallelism centralizes the flag->cap mapping (unset/<=0 => -1 unbounded) and is unit tested. Out of scope (Marten-side follow-up): the StoreOptions.Events .MaxConcurrentRebuildsPerDatabase configuration knob with the NpgsqlConnectionPoolSize/8 derived default, the EnableExtendedProgressionTracking interaction analysis, and the Postgres-backed 8-projection/32-tenant cap regression test all live in the Marten repo (they depend on Npgsql/Marten types not available in JasperFx). The per-tenant rebuild layer is already parameterized by CrossTenantRebuild.maxParallelism for the Marten daemon to pass the same cap through. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Closes #420.
What
Adds a
--max-concurrentflag todotnet run -- projections rebuildand applies it as theMaxDegreeOfParallelismof the per-database rebuild fan-out inProjectionHost.TryRebuildShardsAsync.Previously the fan-out over projections within a database was an unbounded
Parallel.ForEachAsync. On a wide store — many projections, especially underUseTenantPartitionedEventswhere each projection further fans out per tenant — that could spawn enough concurrent rebuild agents to exhaust the connection pool, thrash the buffer cache, and contend onmt_event_progression.MaxDegreeOfParallelism = -1).ProjectionInput.ResolveMaxDegreeOfParallelism()centralizes the flag→cap mapping and is unit tested (7 cases: unset, positive, and the0/negative degenerate cases that would otherwise throw).Tests
ProjectionInputTests— unset → unbounded; positive cap honored; non-positive falls back to unbounded. Full solution compiles clean in Release (net9.0/net10.0).Deliberately out of scope (Marten-side follow-up, can't run in this repo)
The issue's central config knob
StoreOptions.Events.MaxConcurrentRebuildsPerDatabaseand itsNpgsqlConnectionPoolSize / 8derived default live on Marten'sEventGraph/StoreOptions— they depend on Npgsql/Marten types not present in JasperFx. So does theEnableExtendedProgressionTrackinginteraction analysis and the Postgres-backed 8-projection × 32-tenant cap regression test. This PR delivers the JasperFx-side honoring mechanism (CLI flag + fan-out cap + logging); the per-tenant layer is already parameterized viaCrossTenantRebuild.maxParallelismfor Marten's daemon to thread the same cap through.🤖 Generated with Claude Code