[jira] [Commented] (CASSANDRA-13203) UPDATE USING TIMESTAMP can surprisingly append to a list column instead of replace

["Benjamin Lerer (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-13203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15874322#comment-15874322 ] 

Benjamin Lerer commented on CASSANDRA-13203:
--------------------------------------------

One important stuff to understand here is that C* use timestamp to determine what is the latest modification.
By consequence, if you send an update with the same timestamp, C* does not know which one is the latest modification and will try to reconcile the data as follow:
# if one of the modifications is a deletion (tomstone), it wins and the data is marked as deleted
# if none of the modifications is a deletion, the update with the greater value win. If {{A > B}} then A win. If {{B > A}} then B win.

If your list was {{frozen}}, the list with the greater value will win. Due to that it will have been possible that you update had no effect.

As your list are not frozen the situation is even worst.
C* has to deleted the cells of the existing list before inserting the new ones. As a deletion (tombstone) is always the winner C* cannot insert the cells with the same timestamp than the one used to deleted them. To avoid that problem, C* delete the list elements using {{timestamp - 1}} and insert them using {{timestamp}}.

As your original data has been inserted with the same timestamp than your update, the deletion as no effect on the original data (as the deletion timestamp is earlier than the one of the original data) and only the second insertion is taken into account.

Updating data with the same timestamp than the one of the existing data is simply something that you should not do with C*.

Unfortunatly, there are currently noway to make the unfrozen lists behave as the frozen ones in this specific scenario.  
  
 

 

> UPDATE USING TIMESTAMP can surprisingly append to a list column instead of replace
> ----------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-13203
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13203
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: craig mcmillan
>            Assignee: Benjamin Lerer
>            Priority: Minor
>
> {code}
> create table stufflist (id uuid primary key , stuff list<text>);
> insert into stufflist (id, stuff) values (75a01c40-eed9-11e6-930a-939ae9ea5575, ['one']) using timestamp 1000;
> update stufflist using timestamp 1000 set stuff=['one'] where id=75a01c40-eed9-11e6-930a-939ae9ea5575;
> select * from stufflist;
>  id                                   | stuff
> --------------------------------------+----------------
>  75a01c40-eed9-11e6-930a-939ae9ea5575 | ['one', 'one']
> {code}



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