guyinyou opened a new issue, #9713:
URL: https://github.com/apache/rocketmq/issues/9713
### Before Creating the Enhancement Request
- [x] I have confirmed that this should be classified as an enhancement
rather than a bug/feature.
### Summary
Optimize the flush method in DefaultMappedFile to ensure flushed position is
only updated after successful disk flush operation, preventing potential data
loss scenarios.
### Motivation
Currently, the flush method in DefaultMappedFile has a critical data
consistency issue where the flushed position is updated regardless of whether
the actual disk flush operation succeeds or fails. This creates a dangerous
scenario where:
1. The system may incorrectly assume data has been persisted to disk when
it's still only in memory
2. If a system crash occurs after a failed flush but before the next
successful flush, data could be permanently lost
3. This undermines the reliability guarantees that RocketMQ provides for
message persistence
The enhancement is necessary to maintain data integrity and prevent
potential message loss, which is critical for a message queue system that
prides itself on reliability and durability guarantees.
### Describe the Solution You'd Like
Move the `FLUSHED_POSITION_UPDATER.set(this, value)` call inside the try
block of the flush method, ensuring it only executes when the disk flush
operation completes successfully.
**Current problematic implementation:**
```java
try {
// flush operations
this.mappedByteBuffer.force();
this.lastFlushTime = System.currentTimeMillis();
} catch (Throwable e) {
// error handling
}
FLUSHED_POSITION_UPDATER.set(this, value); // Always executes, even on
failure
```
**Proposed solution:**
```java
try {
// flush operations
this.mappedByteBuffer.force();
this.lastFlushTime = System.currentTimeMillis();
FLUSHED_POSITION_UPDATER.set(this, value); // Only executes on success
} catch (Throwable e) {
// error handling - position not updated on failure
}
```
**Additional improvements:**
- Move the `isWriteable()` check to the beginning of the method to avoid
unnecessary operations
- Remove duplicate `isWriteable()` checks for cleaner code structure
### Describe Alternatives You've Considered
1. **Adding explicit success/failure tracking**: Instead of moving the
position update, we could add a boolean flag to track flush success. However,
this would add complexity and the current approach is simpler and more reliable.
2. **Separating position update into a separate method**: We could extract
the position update logic into a dedicated method, but this doesn't solve the
core issue and adds unnecessary abstraction.
3. **Using a different synchronization mechanism**: We could use more
complex synchronization, but the current atomic updater approach is already
optimal for this use case.
4. **Adding additional validation**: We could add checks to verify the flush
actually succeeded, but the try-catch mechanism already provides this
validation naturally.
The chosen solution is the most straightforward and effective approach that
directly addresses the root cause without introducing additional complexity or
performance overhead.
### Additional Context
_No response_
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