[HBASE-21032] ScanResponses contain only one cell each

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.1.0
• Fix Version/s: 3.0.0-alpha-1, 2.2.0, 2.1.1
• Component/s: Performance, Scanners

Environment

HBase 2.1.0

Hadoop 2.8.4

Java 8

• Hadoop Flags: Reviewed
• Assignee: Andrey Elenskiy
• Reporter: Andrey Elenskiy
• Created: 09/Aug/18 18:33
• Updated: 22/Aug/18 13:29
• Resolved: 21/Aug/18 20:32

Description

I have a long row with a bunch of columns that I'm scanning with setAllowPartialResults(true). In the response I'm getting the first partial ScanResponse being around 2MB with multiple cells while all of the consequent ones being 1 cell per ScanResponse. After digging more, I found that each of those single cell ScanResponse partials are preceded by a heartbeat (zero cells). This results in two requests per cell to a regionserver.

I've attached code to reproduce it on hbase version 2.1.0 (it works as expected on 2.0.0 and 2.0.1).

App.java

I'm fairly certain it's a serverside issue as gohbase client is having the same issue. I have not tried to reproduce this with multi-row scan.