zhangkre opened a new issue, #1234:
URL: https://github.com/apache/arrow-java/issues/1234
### Describe the bug, including details regarding any error messages,
version, and platform.
### Problem Description
The VectorUnloader class has serious memory leak issues when serializing
Vector data. Any exception thrown during the process will cause previously
retained ArrowBuf instances to never be released.
Root Cause
ArrowBuf uses reference counting for memory management. After calling
retain(), a corresponding release() must be called to free the buffer. The code
has exception-safety defects in multiple locations:
---
#### Bug 1: OOM during compression causes leak
```
Location: appendNodes() method, around line 75
buf.getReferenceManager().retain();
buffers.add(codec.compress(vector.getAllocator(), buf)); // OOM here causes
leak
Problem: If codec.compress() throws OutOfMemoryError, retain() has already
been called but buffers.add() never executes, making the ArrowBuf unreleasable.
```
---
#### Bug 2: Compression failure in loop causes partial leak
```
Location: appendNodes() method, around lines 78-85
for (ArrowBuf buf : fieldBuffers) {
buf.getReferenceManager().retain();
buffers.add(codec.compress(vector.getAllocator(), buf)); // Any failure
leaks all previously retained buffers
}
Problem: Any compression failure in the loop causes all previously retained
buffers to leak.
```
---
#### Bug 3: Exception during recursive child vector processing causes leak
```
Location: appendNodes() method, around lines 87-89
for (FieldVector child : vector.getChildrenFromFields()) {
appendNodes(child, nodes, buffers, variadicBufferCounts); // Exception
here leaks buffers from current level
}
Problem: An exception during recursive child processing prevents release of
buffers already retained at the current level.
```
---
#### Bug 4: Iteration failure in top-level loop causes cumulative leaks
```
Location: getRecordBatch() method, around lines 53-58
for (FieldVector vector : root.getFieldVectors()) {
appendNodes(vector, nodes, buffers, variadicBufferCounts); // Any
failure leaks all previously retained buffers
}
Problem: Each iteration retains buffers, and any failure causes cumulative
leaks of all previously retained buffers. This is an accumulated leak.
```
---
### Impact
- All code using VectorUnloader.getRecordBatch()
- Leak probability increases significantly when processing large datasets or
when compressor runs low on memory
- Leaked ArrowBuf instances persist until process termination
Suggested Fix
1. Use try-finally to ensure release() is called even when exceptions occur
2. Or add buffers to the list before calling retain() and compress()
3. Use transactional error handling for the entire getRecordBatch()
operation, rolling back all buffers on failure
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