# Changelog: RandomX Mining Optimization

## Summary

Optimizes RandomX miner memory usage by replacing per-thread dataset/cache allocation with a shared `RandomXDatasetManager`. Reduces memory footprint from ~2.3GB × N threads to ~2.3GB total.

## Problem

The original RandomX miner implementation allocated a full RandomX dataset (~2GB) and cache (~256MB) for each mining thread. With multiple threads, this quickly exhausted available memory:

- 4 threads: ~9.2GB
- 8 threads: ~18.4GB
- 16 threads: ~36.8GB

## Solution

Implemented a shared `RandomXDatasetManager` that allocates a single dataset and cache, shared by all miner threads via read-only access (explicitly supported by RandomX design).

## Changes

### `src/miner.cpp`

- **Added `RandomXDatasetManager` class:**
  - Manages a single shared RandomX cache and dataset.
  - Thread-safe key updates using `boost::shared_mutex` (readers-writer lock).
  - `Initialize(key)`: Allocates cache and dataset, initializes with key, builds dataset using all CPU cores.
  - `UpdateKey(newKey)`: Acquires exclusive lock, reinitializes cache with new key, rebuilds dataset.
  - `GetDataset()`: Returns pointer to shared dataset for VM creation.
  - `AcquireSharedLock()` / `ReleaseSharedLock()`: Miner threads hold shared lock while hashing to prevent key updates mid-hash.
  - `Shutdown()`: Releases all RandomX resources.

- **Modified `GenerateBitcoins()`:**
  - Initializes `RandomXDatasetManager` with initial key before spawning miner threads.
  - Calls `Shutdown()` when mining stops.

- **Modified `RandomXMiner()`:**
  - Creates lightweight per-thread VM using shared dataset (`randomx_create_vm(..., manager.GetDataset())`).
  - Acquires shared lock before hashing, releases after.
  - On key rotation: releases shared lock, calls `manager.UpdateKey()`, reacquires shared lock, recreates VM.
  - Cleanup only destroys thread's VM — dataset/cache owned by manager.

## Memory Usage

| Threads | Before | After |
|---------|--------|-------|
| 1 | ~2.3GB | ~2.3GB |
| 4 | ~9.2GB | ~2.3GB |
| 8 | ~18.4GB | ~2.3GB |
| 16 | ~36.8GB | ~2.3GB |

## Thread Safety

- RandomX dataset is read-only after initialization — safe to share across threads.
- `boost::shared_mutex` ensures:
  - Multiple threads can hash concurrently (shared lock).
  - Key updates are exclusive (exclusive lock blocks until all shared locks release).
  - No thread hashes with stale dataset during key change.

## Files Modified

| File | Lines Added | Lines Removed |
|------|-------------|---------------|
| `src/miner.cpp` | ~80 | ~20 |