[IMPALA-5389] Clarify lifetime of DiskIoMgr::BufferDescriptor objects

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Impala 2.9.0
• Fix Version/s: Impala 2.10.0
• Component/s: Backend
• Labels: resource-management
• Target Version: Product Backlog
• Epic Color: ghx-label-6
• Assignee: Tim Armstrong
• Reporter: Tim Armstrong
• Created: 30/May/17 21:41
• Updated: 16/Jun/17 16:24
• Resolved: 16/Jun/17 16:24

Description

The transfer of DiskIoMgr::BufferDescriptor objects between different parts of the code is somewhat subtle. It would be good to enhance the code so that the ownership transfer was more explicit and it was easier to spot errors via inspection or assertions.

Some ideas:

• We could use unique_ptr instead of raw pointers - there is always a single owner of a BufferDescriptor
• We could add a DCHECK to the destructor to ensure it is returned.
• We don't really need to cache and recycle the objects (it's probably a pessimisation compared to TCMalloc's small object caching).

Issue Links

• is depended upon by: IMPALA-4835 HDFS scans should operate with a constrained number of I/O buffers