[I] [Enhancement] Optimize DefaultMappedFile by Replacing RandomAccessFile with FileChannel [rocketmq]

["RongtongJin (via GitHub)" <gi...@apache.org>]

RongtongJin opened a new issue, #9716:
URL: https://github.com/apache/rocketmq/issues/9716

   ### Before Creating the Enhancement Request
   
   - [x] I have confirmed that this should be classified as an enhancement rather than a bug/feature.
   
   
   ### Summary
   
   This issue addresses performance optimization in the `DefaultMappedFile` class by completely replacing `RandomAccessFile` with `FileChannel` for all write operations. The current implementation maintains both I/O mechanisms, which creates unnecessary complexity and reduces performance.
   
   ### Motivation
   
   The existing `DefaultMappedFile` implementation suffers from several performance and maintainability issues:
   
   1. **Performance Bottleneck**: `RandomAccessFile` demonstrates inferior performance compared to `FileChannel` for high-throughput I/O operations, particularly in scenarios involving frequent small writes typical in message queue operations.
   
   2. **Memory Management Inefficiency**: The `SharedByteBuffer` currently uses heap memory allocation (`ByteBuffer.allocate()`), which increases garbage collection pressure and reduces I/O efficiency.
   
   3. **Code Complexity**: Maintaining two distinct I/O code paths increases complexity, making the codebase harder to maintain, debug, and extend.
   
   4. **Resource Management Overhead**: Managing both `RandomAccessFile` and `FileChannel` requires more complex resource cleanup logic and increases the risk of resource leaks.
   
   
   ### Describe the Solution You'd Like
   
   ### Core Implementation Changes
   
   1. **Complete RandomAccessFile Removal**
      - Eliminate the `randomAccessFile` field and all associated logic
      - Simplify resource management by consolidating to a single I/O mechanism
      - Remove RandomAccessFile-related cleanup code in `cleanResources()` and `destroy()` methods
   
   2. **Unified FileChannel I/O Operations**
      - Use `FileChannel` exclusively for all write operations when `writeWithoutMmap` is enabled
      - Maintain backward compatibility by preserving the `writeWithoutMmap` configuration option
      - Fix `SharedByteBuffer` write logic to ensure accurate byte count writing using `result.getWroteBytes()`
   
   3. **Direct Memory Allocation Optimization**
      - Convert `SharedByteBuffer` to use direct memory allocation (`ByteBuffer.allocateDirect()`)
      - Reduce GC pressure and enable zero-copy I/O operations for better performance
   
   4. **Enhanced Error Handling and Configuration**
      - Integrate `RunningFlags` support for improved error handling and recovery mechanisms
      - Refactor constructor design to support additional configuration options while maintaining backward compatibility
   
   ### Technical Implementation Details
   
   **Before (Dual I/O Mechanism):**
   ```java
   if (writeWithoutMmap && randomAccessFile != null) {
       randomAccessFile.seek(currentPos);
       randomAccessFile.write(data, offset, length);
   } else {
       // MappedByteBuffer logic
   }
   ```
   
   **After (Unified FileChannel):**
   ```java
   if (writeWithoutMmap) {
       this.fileChannel.position(currentPos);
       ByteBuffer writeBuffer = ByteBuffer.wrap(data, offset, length);
       this.fileChannel.write(writeBuffer);
   } else {
       // MappedByteBuffer logic (unchanged)
   }
   ```
   
   **Memory Allocation Optimization:**
   ```java
   // Before
   this.buffer = ByteBuffer.allocate(size);
   
   // After  
   this.buffer = ByteBuffer.allocateDirect(size);
   ```
   
   ### Expected Performance Benefits
   
   - **I/O Performance**: 10-20% improvement in write operation throughput
   - **Memory Efficiency**: Reduced GC pressure through direct memory allocation
   - **Code Maintainability**: ~20 lines of code reduction with improved clarity
   - **Operational Consistency**: Unified I/O operations eliminate potential behavioral inconsistencies
   
   ### Describe Alternatives You've Considered
   
   No
   
   ### Additional Context
   
   No


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Re: [I] [Enhancement] Optimize DefaultMappedFile by Replacing RandomAccessFile with FileChannel [rocketmq]

["RongtongJin (via GitHub)" <gi...@apache.org>]

RongtongJin closed issue #9716: [Enhancement] Optimize DefaultMappedFile by Replacing RandomAccessFile with FileChannel
URL: https://github.com/apache/rocketmq/issues/9716


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