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https://issues.apache.org/jira/browse/CASSANDRA-8319?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aleksey Yeschenko resolved CASSANDRA-8319.
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Resolution: Invalid
Apparently this already works. Since 2.0.
> Allow LWT DELETE with column comparison
> ---------------------------------------
>
> Key: CASSANDRA-8319
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8319
> Project: Cassandra
> Issue Type: Improvement
> Components: API, Core
> Reporter: DOAN DuyHai
> Priority: Minor
> Fix For: 2.1.2
>
>
> Right now, the only way to use LWT with DELETE is to rely on the IF NOT
> EXISTS keyword
> There may be some scenarios where using IF column=xxx with DELETE is relevant.
> I am preparing a hands-on with a chat application using C*. A chatroom is
> defined as:
> {code:sql}
> CREATE TABLE chatroom (
> room_id uuid PRIMARY KEY,
> name text,
> participants list<frozen <person>> // person is an UDT representing a
> subset of the users table);
> {code}
> Right now, upon removing a participant from the room, I need to:
> * count remaining participants in the room (read the participants list)
> * remove the room (the whole partition) is there isn't anyone inside
> This is a read-before-write pattern, but even this does not prevent race
> conditions. Indeed, the last participant may leave the room at the same time
> a new one enters
> So using LWT with "DELETE FROM chatroom IF participants = [] WHERE room_id=
> ..." may help making the removal safe
> With this design, room creation/deletion as well as participants
> addition/removal should go through LWT to be consistent. It's slow but
> participant joining and leaving event frequency is low enough compared to
> people posting messages to make the trade off not too expensive in general
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