[KUDU-1808] Simplify KuduSession mutation buffer/flush watermark pct API

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 1.0.0
• Fix Version/s: n/a
• Component/s: client
• Assignee: Alexey Serbin
• Reporter: Matthew Jacobs
• Created: 14/Dec/16 22:12
• Updated: 15/Jun/19 18:13
• Resolved: 15/Jun/19 18:13

Description

The API to configure the KuduSession memory is very confusing. It's not obvious how to pick good values for SetMutationBufferSpace(), SetMutationBufferMaxNum(), and SetMutationBufferFlushWatermark(). My understanding is that a user might:

• pick some amount of memory M to be used for the mutation buffer space, though this isn't obvious (high values increase throughput, but too high and the writes may overwhelm tservers)
• set the flush watermark pct to (1/NumBuffers) where NumBuffers = ( M / 7MB) , and where 7MB is Kudu's internal buffer size
  (formula from tlipcon)
• Set SetMutationBufferMaxNum(0) since the max buffers wouldn't be necessary.

This is what Impala does at the moment, but this is very complicated.