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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-7857) Ability to froze UDT
Date Mon, 01 Sep 2014 11:56:20 GMT
Sylvain Lebresne created CASSANDRA-7857:
-------------------------------------------

             Summary: Ability to froze UDT
                 Key: CASSANDRA-7857
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7857
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Sylvain Lebresne
            Assignee: Sylvain Lebresne
             Fix For: 2.1.0



Currently, UDT are serialized into a single value. For 3.0, we want to change that somewhat
and allow updating individual subfields: CASSANDRA-7423 (and ultimately, we'll probably allow
querying subpart of UDT to some extend). Also for 3.0, we want to allow some nesting of collections
(CASSANDRA-7826).

However, migrating the currently serialized UDT would be challenging. Besides that, even with
nested collections, we probably won't be able to support nesting within map keys and sets
without serializing (at the very least, not initially). Also, it can be useful in some specific
case to have UDT or collections for PK columns, even if those are serialized.

So we need a better way to distinguish when a composite types (collections & UDT) are
serialized (which imply you can't update subpart of the value, you have to rewrite it fully)
and when they are not. The suggestion is then to introduce a new keyword, {{frozen}}, to indicate
that a type is serialized:
{noformat}
CREATE TYPE foo (a int, b int);
CREATE TABLE bar (
    k frozen<foo> PRIMARY KEY,
    m map<frozen<set<int>>, text>
)
{noformat}
A big advantage is that it makes the downside (you can't update the value without rewriting
it all) clear and upfront.

Now, as of 2.1, we only support frozen UDT, and so we should make this clear by 1) adding
the frozen keyword and 2) don't allow use of UDT unless they are "frozen" (since that's all
we really support). This is what this ticket proposes to do. And this should be done in 2.1.0
or this will be a breaking change.

We will have a follow-up ticket that will extend {{frozen}} to collection, but this is less
urgent since this will be strictly an improvement.

I'll note that in term of syntax, {{serialized}} was suggested as an alternative to {{frozen}}.
I personally have a minor preference for {{serialized}} but it was argued that it had a "sequential"
connotation which {{frozen}} don't have. Changing that is still up for discussion, but we
need to reach a decision quickly.





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