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Posted to commits@cassandra.apache.org by "Jonathan Ellis (JIRA)" <ji...@apache.org> on 2015/01/20 19:44:35 UTC
[jira] [Commented] (CASSANDRA-8649) CAS per (partition key +
clustering key) and not only per (partition key)
[ https://issues.apache.org/jira/browse/CASSANDRA-8649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14284185#comment-14284185 ]
Jonathan Ellis commented on CASSANDRA-8649:
-------------------------------------------
I'm inclined to wontfix, but I'll call out [~kohlisankalp] and [~slebresne] for second opinions.
> CAS per (partition key + clustering key) and not only per (partition key)
> -------------------------------------------------------------------------
>
> Key: CASSANDRA-8649
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8649
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: Dobrin
> Fix For: 3.0
>
>
> Reading the description at http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0 :
> ...
> * The columns updated do NOT have to be the same as the columns in the IF clause.
> * Lightweight transactions are restricted to a single partition; this is the granularity at which we keep the internal Paxos state. As a corollary, transactions in different partitions will never interrupt each other.
> ...
> So my understanding of the above is that if multiple writers for example perform CAS inserts (INSERT...IF NOT EXISTS) using the same partition key and different clustering keys will interrupt/interfere with each other?
> Is this understanding correct? (my tests seems to confirm it)
> For example if I want to model users from different country/city/area and I want to be able to list all the users from a given country ordered by (city,area) and also I know that a single cassandra node will be able to store all the users from a given country but I need to partition users from different countries because a single cassandra node will not be enough:
> CREATE COLUMNFAMILY user (
> country text,
> city text,
> area text,
> id text,
> json text,
> version bigint,
> PRIMARY KEY ((country), city, area, id)
> );
> Where id is the user id and json is a JSON serialized user object (an aggregate) containing more information about the user.
> I want to be able to CAS insert many users into the same country concurrently using
> INSERT INTO user(country, city, area, id, json, version) VALUES ('x',...) IF NOT EXISTS;
>
> and be able to CAS update users from the same country concurrently:
> UPDATE user SET json='{...}',version=18 WHERE country='x' AND city='y' AND area='z' AND id='123' IF version=17;
>
> As I understand this will not be efficient because all the above concurrent statements will have to be "ordered" by the same paxos instance/state per country 'x'? (and trying it results in a lot of WriteTimeoutException-s)
> If yes - can we made paxos to support IF statements per column/cell?
> By cell/column I mean all the underlying persistent state that is behind the compound primary key (partition key + clustering key) - in the above example
> the state is json and version
> the partition key is the country
> and the clustering key is (city, area, id)
> (
> I'm stating it explicitly as I'm not completely sure whether this is a single cell or double cells underneath at the storage engine, references used:
> http://www.datastax.com/dev/blog/cql3-for-cassandra-experts
> http://www.datastax.com/dev/blog/does-cql-support-dynamic-columns-wide-rows
> )
> In other words is it possible to make CAS per (partition key + clustering key) and not only per (partition key)?
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