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https://issues.apache.org/jira/browse/CASSANDRA-8649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14285383#comment-14285383
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Dobrin commented on CASSANDRA-8649:
-----------------------------------
Guys, please share some thoughts? Why don't you like it?
\\
I saw with cassandra-cli that a single user CQL row from the above example
{noformat}
country | city | area | id | json | version
---------+------+------+-----+------+---------
x | y | z | 123 | {} | 17
{noformat}
translates into three columns/cells underneath:
RowKey: x
=> (name=y:z:123:, value=, timestamp=1421827135986000)
=> (name=y:z:123:json, value=7b7d, timestamp=1421827135986000)
=> (name=y:z:123:version, value=0000000000000011, timestamp=1421827135986000)
So you do not like it because of the (not so natural/direct) CQL row mapping to
the underlying C* data structures?
\\
I can have two billion users in a partition but accessing them via CAS
statements means they have a common consistency boundary but I nead each user
to be a consistency boundary in its own as my users share nothing.
\\
I can think of at least two ways of how to fix this with the current CAS
support.
First I need a partition per User -> PRIMARY KEY ((country, city, area, id)) in
order to fix the consistency boundary / concurrent access. Then:
1) Maintain an index CF manually:
CREATE COLUMNFAMILY user_index (
country text,
city text,
area text,
id text,
PRIMARY KEY ((country), city, area, id)
);
After each successful CAS insert into the user CF I can do a non-CAS insert
into user_index CF (QUARUM consistency level).
After (or before) successful CAS delete from the user CF I can do a non-CAS
delete into user_index CF (QUARUM consistency level).
CAS Updates do not reflect the index.
\\
This works for me but is not that good as CAS per (partition key+clustering
key) as I need to maintain an additional CF and need not to "forget" to alter
the index when I do insert or delete into the user CF.
\\
OR
\\
2) Use OrderPreservingPartitioner. The keyspace distribution among nodes will
be not balanced.
Maybe I can fix it so that instead of inserting the country I will insert
hash(country) to make the country distribution even or something like this!? ..
I have never tried OrderPreservingPartitioner. But as I see the partitioner is
per cluster and I need it per CF so .. this does not work for me.
\\
Will appreciate any thoughts or more ideas?
> 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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