Limit Velox's global memory manager's usage to 0.75 * Spark overhead memory by default. The overhead memory is calculated by same manner with vanilla Spark.

Velox's global memory manager is used for some global allocations that don't belong to a specific query or task. These allocations are not tracked by Spark task memory manager.

After the patch, spark.memory.offHeap.size and spark.executor.memoryOverhead (with spark.executor.memoryOverheadFactor / spark.executor.minMemoryOverhead for higher version Spark, probably) will co-work for Velox backend's memory management.

1. spark.memory.offHeap.size limits major of the memory allocations happened during Velox query execution, e.g., hash tables, sort buffers, shuffle buffers, etc.
2. spark.executor.memoryOverhead limits the memory allocations that are hardly tracked by Spark task memory manager, or that don't belong to a specific query. E.g., allocations happen during spilling, or possibly the global cache size (unimplemented).

Edit: As the change fails a couple of CI tests, we are setting the internal Velox global poll size limit to Long.MaxValue by default in the PR, to bypass the check for sometime, until the relevant bugs from Velox get fixed.