# WeaselDB Threading Performance Analysis Report

## Summary

WeaselDB achieved 1.3M requests/second throughput using a two-stage ThreadPipeline, with 396ns serial CPU time per request. Higher serial CPU time means more CPU budget available for serial processing.

## Performance Metrics

### Throughput
- Non-blocking: 1.3M requests/second over unix socket
- Blocking: 1.1M requests/second over unix socket
- 8 I/O threads with 8 epoll instances
- Load tester used 12 network threads
- Max latency: 4ms out of 90M requests

### Threading Architecture
- Two-stage pipeline: Stage-0 (noop) → Stage-1 (connection return)
- Lock-free coordination using atomic ring buffer
- Each request "processed" serially on single thread

### Non-blocking vs Blocking Acquisition

**Non-blocking acquisition (`mayBlock=false`)**:
- Throughput: 1.3M requests/second (maintained with up to 1200 loop iterations)
- Stage-0 CPU: 100% (10% futex wake, 90% other)
- Serial CPU time per request: 396ns (1200 iterations, validated with nanobench)
- Theoretical maximum serial CPU time: 769ns (1,000,000,000ns ÷ 1,300,000 req/s)
- Serial efficiency: 51.5% (396ns ÷ 769ns)
- 100% CPU usage when idle

**Blocking acquisition (`mayBlock=true`)**:
- Throughput: 1.1M requests/second (800 loop iterations)
- Stage-0 CPU: 100% total (18% sched_yield, 8% futex wait, 7% futex wake, 67% other)
- Serial CPU time per request: 266ns (800 iterations, validated with nanobench)
- Theoretical maximum serial CPU time: 909ns (1,000,000,000ns ÷ 1,100,000 req/s)
- Serial efficiency: 29.3% (266ns ÷ 909ns)
- 0% CPU usage when idle

### Request Flow
```
I/O Threads (8) → HttpHandler::on_batch_complete() → ThreadPipeline
    ↑                                                        ↓
    |                                                 Stage 0: Noop thread
    |                                                 (396ns serial CPU per request)
    |                                                        ↓
    |                                                 Stage 1: Connection return
    |                                                        ↓
    └─────────────────────── Server::release_back_to_server()
```

### Pipeline Configuration
- Stage 0: 1 noop thread
- Stage 1: 2 worker threads for connection return
- Atomic counters with shared ring buffer

### Memory Management
- Transfer ownership of the connection along the pipeline

## Test Configuration

- Server: test_config.toml with 8 io_threads, 8 epoll_instances
- Load tester: ./load_tester --network-threads 12
- Build: ninja
- Command: ./weaseldb --config test_config.toml
