[KUDU-2867] Optimize Timestamp varint decoding

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.11.0
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 18/Jun/19 07:40
• Updated: 27/Jun/19 06:27
• Resolved: 27/Jun/19 06:27

Description

In looking at a profile with some delta reads, I noticed ~11% of CPU going to GetMemcmpableVarint, much of which is from Timestamp decoding. In practice, any timestamp from HybridClock will need an 8-byte varint, so we can fast-path that case. (unfortunately it's too much effort to change the data format to not use a varint here)