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From "Sylvain Lebresne (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-3625) Do something about DynamicCompositeType
Date Tue, 13 Dec 2011 22:47:30 GMT
Do something about DynamicCompositeType
---------------------------------------

                 Key: CASSANDRA-3625
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3625
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Sylvain Lebresne


Currently, DynamicCompositeType is a super dangerous type. We cannot leave it that way or
people will get hurt.

Let's recall that DynamicCompositeType allows composite column names without any limitation
on what each component type can be. It was added to basically allow to use different rows
of the same column family to each store a different index. So for instance you would have:
{noformat}
index1: {
  "bar":24 -> someval
  "bar":42 -> someval
  "foo":12 -> someval
  ...
}
index2: {
  0:uuid1:3.2 -> someval
  1:uuid2:2.2 -> someval
  ...
}
....
{noformat}
where index1, index2, ... are rows.
So each row have columns whose names have similar structure (so they can be compared), but
between rows the structure can be different (we neve compare two columns from two different
rows).

But the problem is the following: what happens if in the index1 row above, you insert a column
whose name is 0:uuid1 ? There is no really meaningful way to compare "bar":24 and 0:uuid1.
The current implementation of DynamicCompositeType, when confronted with this, says that it
is a user error and throw a MarshalException.
The problem with that is that the exception is not throw at insert time, and it *cannot* be
because of the dynamic nature of the comparator. But that means that if you do insert the
wrong column in the wrong row, you end up *corrupting* a sstable.

It is too dangerous a behavior. And it's probably made worst by the fact that some people
probably think that DynamicCompositeType should be superior to CompositeType since you know,
it's dynamic.

One solution to that problem could be to decide of some random (but predictable) order between
two incomparable component. For example we could design that IntType < LongType < StringType
...

Note that even if we do that, I would suggest renaming the DynamicCompositeType to something
that suggest that CompositeType is always preferable to DynamicCompositeType unless you're
really doing very advanced stuffs.

Opinions?

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