## What changes were proposed in this pull request?
In `UnsafeInMemorySorter`, one record may take 32 bytes: 1 `long` for pointer, 1 `long` for key-prefix, and another 2 `long`s as the temporary buffer for radix sort.
In `UnsafeExternalSorter`, we set the `DEFAULT_NUM_ELEMENTS_FOR_SPILL_THRESHOLD` to be `1024 * 1024 * 1024 / 2`, and hoping the max size of point array to be 8 GB. However this is wrong, `1024 * 1024 * 1024 / 2 * 32` is actually 16 GB, and if we grow the point array before reach this limitation, we may hit the max-page-size error.
Users may see exception like this on large dataset:
```
Caused by: java.lang.IllegalArgumentException: Cannot allocate a page with more than 17179869176 bytes
at org.apache.spark.memory.TaskMemoryManager.allocatePage(TaskMemoryManager.java:241)
at org.apache.spark.memory.MemoryConsumer.allocatePage(MemoryConsumer.java:121)
at org.apache.spark.util.collection.unsafe.sort.UnsafeExternalSorter.acquireNewPageIfNecessary(UnsafeExternalSorter.java:374)
at org.apache.spark.util.collection.unsafe.sort.UnsafeExternalSorter.insertRecord(UnsafeExternalSorter.java:396)
at org.apache.spark.sql.execution.UnsafeExternalRowSorter.insertRow(UnsafeExternalRowSorter.java:94)
...
```
Setting `DEFAULT_NUM_ELEMENTS_FOR_SPILL_THRESHOLD` to a smaller number is not enough, users can still set the config to a big number and trigger the too large page size issue. This PR fixes it by explicitly handling the too large page size exception in the sorter and spill.
This PR also change the type of `spark.shuffle.spill.numElementsForceSpillThreshold` to int, because it's only compared with `numRecords`, which is an int. This is an internal conf so we don't have a serious compatibility issue.
## How was this patch tested?
TODO
Author: Wenchen Fan <wenchen@databricks.com>
Closes#18251 from cloud-fan/sort.
079a2609d7