[ORC-574] Performance: Use const references for string statistics min and max to avoid copy construction

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.6.2
• Fix Version/s: 1.5.9, 1.6.3, 1.7.0
• Component/s: C++
• Assignee: David Zanter
• Reporter: David Zanter
• Created: 04/Dec/19 14:23
• Updated: 31/Jan/20 17:44
• Resolved: 06/Dec/19 16:43

Description

Via Callgrind Performance Profiling of a scenario of a Copy (Full Read and then Full Write) of a 1.9 million row ZLib Compressed ORC Table.  The #4 Usage of CPU is the std::string alloc from being called by: orc::StringColumnStatisticsImpl::update method due to the getMax/getMin calls causing std:string alloc/copy/delete.

 

Changing the getMaximum/getMinimum methods to return const vals will prevent these alloc/copy/deletes from occurring.

 

Currently with 1.6.X master the performance profile of this scenario is:

Instructions Executed: 16.6 Billion Instructions

real clock time 3.91 seconds

 

With the fix to use consts, this improves the CPU usage by about 38% and the Clock Time about 10% to:

Instructions Executed: 12.0 Billion Instructions

real clock time 3.53 seconds

 

Attached JPG showing before (left) and after (right) screenshot of callgrind.

 

 

Issue Links

• links to: GitHub Pull Request #458