[HBASE-25364] Redo the getMidPoint() in HFileWriterImpl to get rid of the double comparison process

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-1, 2.5.0
• Hadoop Flags: Reviewed
• Assignee: Zhuoyue Huang
• Reporter: Zhuoyue Huang
• Created: 06/Dec/20 03:15
• Updated: 14/Feb/21 17:57
• Resolved: 10/Feb/21 16:32

Description

There is a TODO like this "TODO: Redo so only a single pass over the arrays rather than one to  compare and then a second composing midpoint." in getMidpoint()  of class ​HFileWriteImpl​
 
The old logic compares the left byte array and the right byte array twice： 

1. A comparison is performed before composing MinimumMidpointArray
2. During composing of MinimumMidpointArray, bytes were comparing again

 
My optimization  combines them into one

Issue Links

• causes: HBASE-25571 Compilation error in branch-2 after HBASE-25364
• links to: GitHub Pull Request #2741