[CASSANDRA-15215] VIntCoding should read and write more efficiently

• Type: Bug
• Status: Open
• Priority: Normal
• Resolution: Unresolved
• Fix Version/s: 3.0.x, 3.11.x, 4.x
• Component/s: Local/Compaction, Local/SSTable
• Bug Category: Degradation - Performance Bug/Regression
• Severity: Normal
• Complexity: Normal
• Discovered By: Code Inspection
• Platform: All
• Assignee: Unassigned
• Reporter: Benedict Elliott Smith
• Created: 16/Jul/19 09:36
• Updated: 29/Oct/19 19:23

Description

Most vints occupy significantly fewer than 8 bytes, and most buffers have >= 8 bytes spare, in which case we can construct the relevant bytes in a register and memcpy them to the correct position. Since we read and write a lot of vints, this waste is probably measurable, particularly during compaction and flush, and can probably be considered a performance bug.