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Sylvain Lebresne commented on CASSANDRA-4179:
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Looking at that more closely, there is a few details on which to decide. At
least:
* Do we care about allowing to add new columns to a composite row key? I guess
since we decided to not support it for composite comparators, it's consistent
to just say we don't support it here. But I'll just note that if we want to
support it that's not trivial because row key with one element won't be
composite underneath so we won't be able to "extend" them.
* What about thrift? This require changing key_alias to be key_aliases. Should
we just say that from thrift you can only see/set the first key alias even if
there are more than one? If we do that, working with those table from thrift
will be more difficult though. That is really the same problem that discussed
in CASSANDRA-4377, do we care than thrift client might not have enough
information to work with CQL3 table correctly?
> Add more general support for composites (to row key, column value)
> ------------------------------------------------------------------
>
> Key: CASSANDRA-4179
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4179
> Project: Cassandra
> Issue Type: Sub-task
> Components: API
> Reporter: Sylvain Lebresne
> Assignee: Sylvain Lebresne
> Priority: Minor
>
> Currently CQL3 have a nice syntax for using composites in the column name
> (it's more than that in fact, it creates a whole new abstraction but let's
> say I'm talking implementation here). There is however 2 other place where
> composites could be used (again implementation wise): the row key and the
> column value. This ticket proposes to explore which of those make sense for
> CQL3 and how.
> For the row key, I really think that CQL support makes sense. It's very
> common (and useful) to want to stuff composite information in a row key.
> Sharding a time serie (CASSANDRA-4176) is probably the best example but there
> is other.
> For the column value it is less clear. CQL3 makes it very transparent and
> convenient to store multiple related values into multiple columns so maybe
> composites in a column value is much less needed. I do still see two cases
> for which it could be handy:
> # to save some disk/memory space, if you do know it makes no sense to
> insert/read two value separatly.
> # if you want to enforce that two values should not be inserted separatly.
> I.e. to enforce a form of "constraint" to avoid programatic error.
> Those are not widely useful things, but my reasoning is that if whatever
> syntax we come up for "grouping" row key in a composite trivially extends to
> column values, why not support it.
> As for syntax I have 3 suggestions (that are just that, suggestions):
> # If we only care about allowing grouping for row keys:
> {noformat}
> CREATE TABLE timeline (
> name text,
> month int,
> ts timestamp,
> value text,
> PRIMARY KEY ((name, month), ts)
> )
> {noformat}
> # A syntax that could work for both grouping in row key and colum value:
> {noformat}
> CREATE TABLE timeline (
> name text,
> month int,
> ts timestamp,
> value1 text,
> value2 text,
> GROUP (name, month) as key,
> GROUP (value1, value2),
> PRIMARY KEY (key, ts)
> )
> {noformat}
> # An alternative to the preceding one:
> {noformat}
> CREATE TABLE timeline (
> name text,
> month int,
> ts timestamp,
> value1 text,
> value2 text,
> GROUP (name, month) as key,
> GROUP (value1, value2),
> PRIMARY KEY (key, ts)
> ) WITH GROUP (name, month) AS key
> AND GROUP (value1, value2)
> {noformat}
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