# max_validation_batches Parameter Implementation

## Summary

Added `max_validation_batches` parameter to limit validation memory usage as a workaround for Candle's lack of CUDA memory clearing APIs.

**Problem**: Validation needs 1760MB for 176 batches, but only 2485MB available → OOM
**Solution**: Limit validation to 50 batches → reduces memory to 500MB → fits in available memory

## Files Modified

### 1. `/home/jgrusewski/Work/foxhunt/ml/examples/train_tft_parquet.rs`

**Line 162-166**: Added CLI parameter
```rust
/// Maximum validation batches to run (default: unlimited, use 50 for 4GB GPUs)
/// Limits validation to N batches to reduce memory usage. Each batch uses ~10MB,
/// so 50 batches = ~500MB vs 1760MB for full validation (176 batches).
#[arg(long)]
max_validation_batches: Option<usize>,
```

**Line 197-201**: Added logging for the parameter
```rust
if let Some(max_val_batches) = opts.max_validation_batches {
    info!("  • Max validation batches: {} (memory optimization)", max_val_batches);
} else {
    info!("  • Max validation batches: unlimited");
}
```

**Line 288**: Added to config construction
```rust
max_validation_batches: opts.max_validation_batches,
```

### 2. `/home/jgrusewski/Work/foxhunt/ml/src/trainers/tft.rs`

**Line 449-452**: Added field to `TFTTrainerConfig`
```rust
/// Maximum validation batches to run (None = unlimited)
/// Limits validation to N batches to reduce memory usage on constrained GPUs.
/// Example: 50 batches = ~500MB vs 1760MB for full validation (176 batches)
pub max_validation_batches: Option<usize>,
```

**Line 482**: Added to Default implementation
```rust
max_validation_batches: None, // Default: unlimited (use all validation data)
```

**Line 522-523**: Added to `to_training_config()` method
```rust
validation_batch_size: self.validation_batch_size,
max_validation_batches: self.max_validation_batches,
```

**Line 1468-1470**: Modified validation loop to limit batches
```rust
// Limit validation batches if max_validation_batches is set (memory optimization)
let max_batches = self.training_config.max_validation_batches.unwrap_or(usize::MAX);
for (i, batch) in val_loader.iter().take(max_batches).enumerate() {
```

**Line 1521-1527**: Added logging when validation is limited
```rust
// Log if validation was limited for memory optimization
if let Some(max) = self.training_config.max_validation_batches {
    info!(
        "[VALIDATION] Processed {} batches (limited to {} for memory optimization)",
        batch_count, max
    );
}
```

### 3. `/home/jgrusewski/Work/foxhunt/ml/src/tft/training.rs`

**Line 58-61**: Added field to `TFTTrainingConfig`
```rust
/// Maximum validation batches to run (None = unlimited)
/// Limits validation to N batches to reduce memory usage on constrained GPUs.
/// Example: 50 batches = ~500MB vs 1760MB for full validation (176 batches)
pub max_validation_batches: Option<usize>,
```

**Line 105**: Added to Default implementation
```rust
max_validation_batches: None, // Default: unlimited (use all validation data)
```

### 4. `/home/jgrusewski/Work/foxhunt/ml/src/benchmark/tft_benchmark.rs`

**Line 554**: Added to benchmark config
```rust
max_validation_batches: None, // Benchmark uses all validation data
```

### 5. `/home/jgrusewski/Work/foxhunt/ml/src/bin/train_tft.rs`

**Line 203**: Added to legacy train_tft config
```rust
max_validation_batches: None, // Default: unlimited validation
```

## Usage

### Command Line
```bash
# Train with limited validation (50 batches for 4GB GPUs)
cargo run -p ml --example train_tft_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 50 \
  --max-validation-batches 50

# Train with unlimited validation (default)
cargo run -p ml --example train_tft_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 50
```

### Expected Impact

With `--max-validation-batches 50`:
- **Validation memory**: ~500MB (vs 1760MB for 176 batches)
- **Available memory**: 2485MB
- **Total usage**: 1611MB (training) + 500MB (validation) = 2111MB < 2485MB ✅
- **Trade-off**: Validation on subset (28% of data), but training still uses all data

### Verification

```bash
# Check compilation
cargo check -p ml --example train_tft_parquet

# Test the parameter
cargo run -p ml --example train_tft_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_small.parquet \
  --epochs 3 \
  --max-validation-batches 10
```

Expected log output:
```
  • Max validation batches: 10 (memory optimization)
...
[VALIDATION] Processed 10 batches (limited to 10 for memory optimization)
```

## Implementation Notes

1. **Two Config Structs**: The implementation spans both `TFTTrainerConfig` (high-level API) and `TFTTrainingConfig` (internal training state).

2. **Default Behavior**: When `max_validation_batches` is `None`, the system processes all validation batches (backward compatible).

3. **Memory Savings**: Each validation batch uses ~10MB, so limiting to 50 batches saves ~1260MB (126 batches × 10MB).

4. **Validation Quality**: With 50 batches, you still validate on ~28% of data, which provides reasonable accuracy estimates while avoiding OOM.

## Testing

All changes compile successfully:
```bash
cargo check -p ml
# Output: Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.27s
```

## Status

✅ **COMPLETE** - All 5 files modified, all compilation errors resolved.