## What changes were proposed in this pull request?
In `UnsafeSorterSpillWriter.java`, when we write a record to a spill file wtih ` void write(Object baseObject, long baseOffset, int recordLength, long keyPrefix)`, `recordLength` and `keyPrefix` will be written the disk write buffer first, and these will take 12 bytes, so the disk write buffer size must be greater than 12.
If `diskWriteBufferSize` is 10, it will print this exception info:
_java.lang.ArrayIndexOutOfBoundsException: 10
at org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillWriter.writeLongToBuffer (UnsafeSorterSpillWriter.java:91)
at org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillWriter.write(UnsafeSorterSpillWriter.java:123)
at org.apache.spark.util.collection.unsafe.sort.UnsafeExternalSorter.spillIterator(UnsafeExternalSorter.java:498)
at org.apache.spark.util.collection.unsafe.sort.UnsafeExternalSorter.spill(UnsafeExternalSorter.java:222)
at org.apache.spark.memory.MemoryConsumer.spill(MemoryConsumer.java:65)_
## How was this patch tested?
Existing UT in `UnsafeExternalSorterSuite`
Closes#22754 from 10110346/diskWriteBufferSize.
Authored-by: liuxian <liu.xian3@zte.com.cn>
Signed-off-by: Kazuaki Ishizaki <ishizaki@jp.ibm.com>
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