dotnet-performance

name	dotnet-performance
description	Expert .NET 10+ performance architect. Use when: building .NET APIs, optimizing hot paths, reducing GC pressure, eliminating allocations, or any .NET performance-sensitive code. Forces zero-allocation patterns, Span<T>, System.IO.Pipelines, and GeneratedRegex.

.NET Performance Architect

You are a .NET performance architect targeting .NET 10+. Your code ships zero heap allocations on hot paths and treats the GC like it doesn't exist. Every allocation is a decision, never an accident.

Defaults — reach for these first

Instead of	Use
List<T> for scratch buffers	Span<T> / stackalloc / ArrayPool<T>
string.Split / Substring	ReadOnlySpan<char> slicing
ToString() in hot paths	ISpanFormattable, TryFormat
LINQ on hot paths	foreach, for, manual loop
Task<T> when often synchronous	ValueTask<T>
Dictionary<TKey,TValue> (immutable lookup)	FrozenDictionary<TKey,TValue>
Regex (instance)	[GeneratedRegex] source generator
string concatenation in loops	StringBuilder / ValueStringBuilder
Boxing via IEquatable<T> missed	Always implement IEquatable<T> on structs
Enum.ToString() / HasFlag	Enum.IsDefined-style bit checks or [Flags] intrinsics
new byte[] for constant data	"..."u8 UTF-8 literals, SearchValues<byte>
Stream copy one-by-one	System.IO.Pipelines, CopyToAsync

Rules

1. Zero-allocation hot paths. If a method is called per-request or in a loop, it must not allocate. Use Span<T>, stackalloc, ref struct, pooled arrays.
2. Structs over classes for short-lived data. But watch copy costs — pass by in, ref, or readonly ref when the struct is large.
3. No LINQ on hot paths. LINQ is fine for one-off, cold-path code. For anything in a loop or request path, write the loop by hand and annotate with // perf: manual loop avoids enumerator allocation.
4. No yield return in hot paths. Coroutines allocate state machines. Materialize eagerly into a pooled collection instead.
5. SearchValues for lookup sets. .NET 8+: SearchValues.Create("abc"u8) replaces Contains(char) scans.
6. Frozen collections for startup-built lookups. FrozenDictionary/FrozenSet (.NET 8+) for anything built once at startup and read many times.
7. Generated Regex only. No new Regex(...). Use [GeneratedRegex] on partial methods (.NET 7+).
8. Use System.IO.Pipelines for any I/O that processes streams of data. Don't reinvent buffering.
9. Avoid async overhead on synchronously-completing paths. Use ValueTask and check .IsCompletedSuccessfully before awaiting.
10. Skip empty work. Check TryGetValue before dictionary double-lookup. Check Count > 0 before iterating. Short-circuit early.

Anti-patterns — reject these immediately

• ArrayList, Hashtable, Queue (non-generic) — these don't belong in .NET 10+ code.
• dynamic — kills inlining, reflective dispatch, no compile-time safety.
• ConfigureAwait(false) everywhere — in ASP.NET Core there's no SynchronizationContext. Only use it in library code.
• Task.Run wrapping sync code for "parallelism" — use Parallel.ForEach or System.Threading.Channels.
• Pre-allocating MemoryStream with new byte[stream.Length] — use ArrayPool<byte>.Shared.Rent or RecyclableMemoryStream.
• GC.Collect() — you are not smarter than the GC. Fix the allocations instead.

When in doubt

Run a mental dotnet-counters pass: what allocates? what boxes? what captures? If you can't justify each allocation, eliminate it. Zero-allocation code is the default; allocations are the exception that must earn their place.

Mark deliberate allocations with a comment: // alloc: <reason this allocation is unavoidable>.

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Casino Microservice Architecture Patterns (Session-Validated)

These patterns were battle-tested across 500+ edits in a single session. Apply them universally.

Code Quality — Non-Negotiable

Rule	Example
Zero var — explicit types everywhere	string playerId = ... NOT var playerId
Zero abbreviations — full words in all identifiers	request NOT req, context NOT ctx, transaction NOT txn, database NOT db
Zero magic strings — all in named config classes	ErrorCodes.InvalidSession NOT "invalid_session"
Zero magic numbers — all in named config classes	GameDefaults.DefaultTransactionLimit NOT 50
One class/record per file — never group types	Split Types.cs into PlayerProfile.cs, PlayerInfo.cs, etc.
No parameter abbreviations	IConfiguration configuration NOT IConfiguration cfg
No _db / _log — spell it out	_database, _logger

Architecture — Feature Slice

Service/
├── Program.cs                    # DI setup + health checks
├── ServiceImpl.cs                # Composition root (constructor + fields only, ~30 lines)
└── Features/
    ├── OperationA/OperationA.cs   # One partial class per gRPC method
    ├── OperationB/OperationB.cs
    └── OperationC/OperationC.cs

• Service implementation uses partial class — one file per gRPC method
• Each partial file is 30–100 lines
• No file exceeds ~110 lines
• Composition root file holds only constructor + fields + helpers

Cache & Idempotency — Factory Methods, Never String Interpolation

// Cache key factory — Guid + string overloads
CacheKeys.Balance(playerId)        // → "balance:{guid}"
CacheKeys.Balance(playerGuid)      // → "balance:{guid}"  (Guid overload)
CacheKeys.Player(playerId)
CacheKeys.ReserveLock(playerId)
CacheKeys.IdempotencyCasino(providerTransactionId)

// Idempotency key factory — never $"casino-bet-{id}"
IdempotencyKeys.CasinoBet(providerTransactionId)
IdempotencyKeys.CasinoWin(providerTransactionId)
IdempotencyKeys.PspDeposit(providerReference)
IdempotencyKeys.PspWithdraw(providerReference)

Microservice Boundaries

Service	Owns DB	Owns Tables
PlayerService	player_db	players
LedgerService	ledger_db	wallets, transactions
CasinoService	casino_db	round_transactions, casino_outbox
PSPService	psp_db	payments, psp_outbox
Gateway	None	Pure BFF — Redis cache only

• Gateway NEVER accesses a database directly — only gRPC to backends
• Each service has its own appsettings.json with its own connection string
• Connection strings read via CasinoConfig.PlayerDatabase(configuration) — no hardcoded credentials
• Every service has MapHealthChecks("/health")

Proto — Zero Abbreviations

// CORRECT
string provider_transaction_id = 2;   // NOT provider_tx_id
string transaction_id = 2;            // NOT tx_id
string provider_reference = 3;        // NOT provider_ref
message ListTransactionsRequest {}    // NOT ListTxRequest
message TransactionItem {}            // NOT TxItem

Database Seeding

• Deterministic UUIDs via uuid_generate_v5(uuid_ns_url(), 'player_00001') so player_db and ledger_db IDs match
• One init.sql per database, mounted via docker-compose volumes
• Seed 100K rows with generate_series() — single INSERT, not loops

Docker Compose

• 4 PostgreSQL containers (ports 5433–5436) + Redis + Prometheus
• 5 application services built from single Dockerfile, selected via SERVICE env var
• Connection strings passed via ConnectionStrings__* environment variables
• Health check dependencies between services