# Log4j2 Benchmark Tool

A minimal Java tool to benchmark Log4j2 logging throughput with configurable concurrent threads and various logging configurations.

## Features

- Configurable number of concurrent logging threads
- Duration-based or event-count-based test modes
- Configurable message size (~100 chars default)
- Multiple Log4j2 configurations to compare:
  - `sync-immediate` - Synchronous with immediateFlush=true
  - `sync-buffered` - Synchronous with immediateFlush=false (8KB buffer)
  - `async-1k` - AsyncLogger with 1024 ring buffer size
  - `async-4k` - AsyncLogger with 4096 ring buffer size
  - `async-10k` - AsyncLogger with 10240 ring buffer size
- CSV output support for further analysis

## Requirements

- Java 17+
- Maven 3.6+

## Build

```bash
mvn clean package
```

This creates an executable fat JAR at `target/log4jbench-1.0-SNAPSHOT.jar` (~2.7MB).

## Usage

### Basic Run (all configs, 100 threads, 10s duration)

```bash
# With Maven
mvn exec:java

# With standalone JAR
java -jar target/log4jbench-1.0-SNAPSHOT.jar
```

### With Custom Options

```bash
java -jar target/log4jbench-1.0-SNAPSHOT.jar --threads=8 --duration=30 --warmup=5
```

### Event-Count Mode

```bash
java -jar target/log4jbench-1.0-SNAPSHOT.jar --mode=events --events=500000 --threads=2
```

### Test Specific Configs Only

```bash
java -jar target/log4jbench-1.0-SNAPSHOT.jar --configs=sync-immediate,async-4k
```

### Custom Message Size

```bash
java -jar target/log4jbench-1.0-SNAPSHOT.jar --msg-size=200 --threads=4
```

### Export to CSV

```bash
java -jar target/log4jbench-1.0-SNAPSHOT.jar --output=results.csv
```

## Command Line Options

| Option | Description | Default |
|--------|-------------|---------|
| `-t, --threads=N` | Number of concurrent threads | 100 |
| `-m, --mode=MODE` | Test mode: `duration` or `events` | duration |
| `-d, --duration=N` | Test duration in seconds | 10 |
| `-e, --events=N` | Total events (events mode) | 1000000 |
| `-w, --warmup=N` | Warmup duration in seconds | 3 |
| `-s, --msg-size=N` | Message size in characters | 100 |
| `-c, --configs=LIST` | Comma-separated config names | all |
| `-o, --output=FILE` | Output CSV file | stdout only |

## Example Output

```
=== Log4j2 Benchmark ===
Threads: 4 | Mode: DURATION | Message size: 100 chars
Duration: 10s | Warmup: 3s
Configs: [sync-immediate, sync-buffered, async-1k, async-4k, async-10k]

Running: sync-immediate ...
sync-immediate   |   4 threads |    1,234,567 events | 10.00s | 123,456 events/s | 12.34 MB/s

Running: async-4k ...
async-4k         |   4 threads |    5,678,901 events | 10.00s | 567,890 events/s | 56.78 MB/s
```

## Log Configurations

### sync-immediate
Standard synchronous file appender with `immediateFlush="true"`. Every log event is flushed to disk immediately.

### sync-buffered
Synchronous file appender with `immediateFlush="false"` and 8KB buffer. Events are batched before writing.

### async-1k / async-4k / async-10k
Async loggers using LMAX Disruptor with ring buffer sizes of 1024, 4096, and 10240 respectively. Logging threads hand off events to a background thread for I/O.

## Notes

- **Cache dropping**: Before each test, the tool attempts to drop Linux filesystem caches (`sync; echo 3 > /proc/sys/vm/drop_caches`) for consistent results. Run with `sudo` for this to work.
- **Async loggers**: Use the LMAX Disruptor for high-throughput async logging.

## License

MIT