C. Scott Andreas updated CASSANDRA-6123:
    Component/s: CQL

> Break timestamp ties consistently for a given user requests
> -----------------------------------------------------------
>                 Key: CASSANDRA-6123
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6123
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: CQL
>            Reporter: Sylvain Lebresne
>            Priority: Major
>             Fix For: 4.x
> The basic goal of this issue is to fix the fact that if 2 different clients 
> issue "simultaneously" the 2 following updates:
> {noformat}
> INSERT INTO foo(k, v1, v2) VALUES (0, 1, -1); // client1
> INSERT INTO foo(k, v1, v2) VALUES (0, -1, 1); // client2
> {noformat}
> then, if both updates get the same timestamp, then currently, we don't 
> guarantee that at the end the sum of {{v1}} and {{v2}} will be 0 (it won't be 
> in that case).
> The idea to solves this is to make sure 2 updates *never* get the same 
> "timestamp" by making the timestamp be the sum of the current time (and we 
> can relatively easily make sur no 2 update coordinated by the same node have 
> the same current time) and a small ID unique to each server node. We can 
> generate this small unique server id thanks to CAS (see CASSANDRA-6108).
> Let's note that this solution is only for server-side generated timestamps.  
> Client provided timestamp will still be allowed, but in that case it will be 
> the job of the client to synchronize to not generate 2 identical timestamp if 
> they care about this behavior.
> Note: see CASSANDRA-6106 for some related discussion on this issue.

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