[CASSANDRA-14323] Same timestamp insert conflict resolution breaks row-level data consistency

• Type: Bug
• Status: Resolved
• Priority: Low
• Resolution: Won't Fix
• Component/s: Legacy/Core
• Severity: Low
• Assignee: Unassigned
• Reporter: Rishi Kathera
• Created: 19/Mar/18 07:02
• Updated: 16/Apr/19 09:29
• Resolved: 20/Mar/18 08:48

Description

When inserting multiple rows with the same primary key and timestamp, memtable update logic does not maintain row-level consistency for the key inserted. For example,

create table test.consistency(pk int PRIMARY KEY , nk1 text, nk2 text);
BEGIN UNLOGGED BATCH USING TIMESTAMP 1521080773000 
insert into test.consistency (pk,nk1,nk2) VALUES (2,'nk1','nk2'); 
insert into test.consistency (pk,nk1,nk2) VALUES (2,'nk2','nk1'); 
APPLY BATCH; 
select * from test.consistency;

In this case, I would expect either one row overwrites the other so the result of the read would be either

2, nk1, nk2

or

2, nk2, nk1

but the row retrieved is

2, nk2, nk2

 which breaks consistency of the writes. This behavior comes from this logic, 

https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/db/Conflicts.java#L45

where it appears that the value of the cell itself is used to resolve overwrite conflict which I don't think is the correct way of handling the situation. Shouldn't it either be overwrite or not overwrite for all cases?