docs: remove outdated document

api/core/workflow/docs/WORKER_POOL_CONFIG.md

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-# GraphEngine Worker Pool Configuration
-
-## Overview
-
-The GraphEngine now supports **dynamic worker pool management** to optimize performance and resource usage. Instead of a fixed 10-worker pool, the engine can:
-
-1. **Start with optimal worker count** based on graph complexity
-1. **Scale up** when workload increases
-1. **Scale down** when workers are idle
-1. **Respect configurable min/max limits**
-
-## Benefits
-
-- **Resource Efficiency**: Uses fewer workers for simple sequential workflows
-- **Better Performance**: Scales up for parallel-heavy workflows
-- **Gevent Optimization**: Works efficiently with Gevent's greenlet model
-- **Memory Savings**: Reduces memory footprint for simple workflows
-
-## Configuration
-
-### Configuration Variables (via dify_config)
-
-| Variable | Default | Description |
-|----------|---------|-------------|
-| `GRAPH_ENGINE_MIN_WORKERS` | 1 | Minimum number of workers per engine |
-| `GRAPH_ENGINE_MAX_WORKERS` | 10 | Maximum number of workers per engine |
-| `GRAPH_ENGINE_SCALE_UP_THRESHOLD` | 3 | Queue depth that triggers scale up |
-| `GRAPH_ENGINE_SCALE_DOWN_IDLE_TIME` | 5.0 | Seconds of idle time before scaling down |
-
-### Example Configurations
-
-#### Low-Resource Environment
-
-```bash
-export GRAPH_ENGINE_MIN_WORKERS=1
-export GRAPH_ENGINE_MAX_WORKERS=3
-export GRAPH_ENGINE_SCALE_UP_THRESHOLD=2
-export GRAPH_ENGINE_SCALE_DOWN_IDLE_TIME=3.0
-```
-
-#### High-Performance Environment
-
-```bash
-export GRAPH_ENGINE_MIN_WORKERS=2
-export GRAPH_ENGINE_MAX_WORKERS=20
-export GRAPH_ENGINE_SCALE_UP_THRESHOLD=5
-export GRAPH_ENGINE_SCALE_DOWN_IDLE_TIME=10.0
-```
-
-#### Default (Balanced)
-
-```bash
-# Uses defaults: min=1, max=10, threshold=3, idle_time=5.0
-```
-
-## How It Works
-
-### Initial Worker Calculation
-
-The engine analyzes the graph structure at startup:
-
-- **Sequential graphs** (no branches): 1 worker
-- **Limited parallelism** (few branches): 2 workers
-- **Moderate parallelism**: 3 workers
-- **High parallelism** (many branches): 5 workers
-
-### Dynamic Scaling
-
-During execution:
-
-1. **Scale Up** triggers when:
-
-   - Queue depth exceeds `SCALE_UP_THRESHOLD`
-   - All workers are busy and queue has items
-   - Not at `MAX_WORKERS` limit
-
-1. **Scale Down** triggers when:
-
-   - Worker idle for more than `SCALE_DOWN_IDLE_TIME` seconds
-   - Above `MIN_WORKERS` limit
-
-### Gevent Compatibility
-
-Since Gevent patches threading to use greenlets:
-
-- Workers are lightweight coroutines, not OS threads
-- Dynamic scaling has minimal overhead
-- Can efficiently handle many concurrent workers
-
-## Migration Guide
-
-### Before (Fixed 10 Workers)
-
-```python
-# Every GraphEngine instance created 10 workers
-# Resource waste for simple workflows
-# No adaptation to workload
-```
-
-### After (Dynamic Workers)
-
-```python
-# GraphEngine creates 1-5 initial workers based on graph
-# Scales up/down based on workload
-# Configurable via environment variables
-```
-
-### Backward Compatibility
-
-The default configuration (`max=10`) maintains compatibility with existing deployments. To get the old behavior exactly:
-
-```bash
-export GRAPH_ENGINE_MIN_WORKERS=10
-export GRAPH_ENGINE_MAX_WORKERS=10
-```
-
-## Performance Impact
-
-### Memory Usage
-
-- **Simple workflows**: ~80% reduction (1 vs 10 workers)
-- **Complex workflows**: Similar or slightly better
-
-### Execution Time
-
-- **Sequential workflows**: No change
-- **Parallel workflows**: Improved with proper scaling
-- **Bursty workloads**: Better adaptation
-
-### Example Metrics
-
-| Workflow Type | Old (10 workers) | New (Dynamic) | Improvement |
-|--------------|------------------|---------------|-------------|
-| Sequential | 10 workers idle | 1 worker active | 90% fewer workers |
-| 3-way parallel | 7 workers idle | 3 workers active | 70% fewer workers |
-| Heavy parallel | 10 workers busy | 10+ workers (scales up) | Better throughput |
-
-## Monitoring
-
-Log messages indicate scaling activity:
-
-```shell
-INFO: GraphEngine initialized with 2 workers (min: 1, max: 10)
-INFO: Scaled up workers: 2 -> 3 (queue_depth: 4)
-INFO: Scaled down workers: 3 -> 2 (removed 1 idle workers)
-```
-
-## Best Practices
-
-1. **Start with defaults** - They work well for most cases
-1. **Monitor queue depth** - Adjust `SCALE_UP_THRESHOLD` if queues back up
-1. **Consider workload patterns**:
-   - Bursty: Lower `SCALE_DOWN_IDLE_TIME`
-   - Steady: Higher `SCALE_DOWN_IDLE_TIME`
-1. **Test with your workloads** - Measure and tune
-
-## Troubleshooting
-
-### Workers not scaling up
-
-- Check `GRAPH_ENGINE_MAX_WORKERS` limit
-- Verify queue depth exceeds threshold
-- Check logs for scaling messages
-
-### Workers scaling down too quickly
-
-- Increase `GRAPH_ENGINE_SCALE_DOWN_IDLE_TIME`
-- Consider workload patterns
-
-### Out of memory
-
-- Reduce `GRAPH_ENGINE_MAX_WORKERS`
-- Check for memory leaks in nodes