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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