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From Silvère Lestang <silvere.lest...@gmail.com>
Subject Re: Multi-type column values in single CF
Date Mon, 04 Jul 2011 08:48:57 GMT
We do pretty much the same thing here, dynamic column with a timestamp for
column name and a different value type for each row. We use the
serialization/deserialization classes provided with Hector and store the
type of the value in the key of the row. Example of row key:
"b6c8a1e7281761e62230ea76daa3d841#INT" => every values are Integer
"7f30a6a2bbb1b921afc8216d8c5d9257#DOUBLE" => every values are Double
....
If I'll have to do it again, I'll try to use (Dynamic)CompositeType for
value or an equivalent mechanism as suggested by Roland.

On 3 July 2011 15:07, Roland Gude <roland.gude@yoochoose.com> wrote:

> You could do the serialization for all your supported datatypes yourself
> (many libraries for serialization are available and a pretty thorough
> benchmarking for them can be found here:
> https://github.com/eishay/jvm-serializers/wiki) and prepend the serialized
> bytes with an identifier for your datatype.
> This would not avoid casting though but would still be better performing
> then serializing to strings as it is done in your example.
> Prepending the values with the id seems to be better to me, because you can
> be sure that a new insertion to some field overwrites the correct column
> even if it changed the type.
>
> -----Ursprüngliche Nachricht-----
> Von: osishkin osishkin [mailto:osishkin@gmail.com]
> Gesendet: Sonntag, 3. Juli 2011 13:52
> An: user@cassandra.apache.org
> Betreff: Multi-type column values in single CF
>
> Hi all,
>
> I need to store column values that are of various data types in a
> single column family, i.e I have column values that are integers,
> others that are strings, and maybe more later. All column names are
> strings (no comparator problem for me).
> The thing is I need to store unstructured data - I do not have fixed
> and known-in-advacne column names, so I can not use a fixed static map
> for casting the values back to their original type on retrieval from
> cassandra.
>
> My immediate naive thought is to simply prefix every column name with
> the type the value needs to be cast back to.
> For example i'll do the follwing conversion to the columns of some key -
> {'attr1': 'val1','attr2': 100}  ~> {'str_attr1' : 'val1', 'int_attr2' :
> '100'}
> and only then send it to cassandra. This way I know to what should I
> cast it back.
>
> But all this casting back and forth on the client side seems to me to
> be very bad for performance.
> Another option is to split the columns on dedicated column families
> with mathcing validation types - a column family for integer values,
> one for string, one for timestamp etc.
> But that does not seem very efficient either (and worse for any
> rollback mechanism), since now I have to perform several get calls on
> multiple CFs where once I had only one.
>
> I thought perhaps someone has encountered a similar situation in the
> past, and can offer some advice on the best course of action.
>
> Thank you,
> Osi
>
>
>

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