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From Bill de hOra <b...@dehora.net>
Subject Re: list of columns
Date Mon, 17 May 2010 14:34:34 GMT
 > But then you'd need
 > re-ahead to check if the column is new,

that should be 'read-ahead', sorry.

Bill

Bill de hOra wrote:
> Agree with David, it's not there and thinking about how the data is laid 
> out on disk, it can't be done without changing core code or harming 
> something else.
> 
>  > if this is a performance concern
> 
> It's not, it was to supply an administrative function on SuperColumns, 
> but it would be good to not crush a node.
> 
>  > a separate column family which just contains the column names and
>  > timestamps with empty values.
> 
> Eventually, you'd want to ask a client library to do this, at the cost 
> of two writes everytime you add a new column. But then you'd need 
> re-ahead to check if the column is new, which would kill write performance.
> 
> Bill
> 
> 
> Jonathan Shook wrote:
>> I think you are correct, David. What Bill is asking for specifically
>> is not in the API.
>>
>> Bill,
>> if this is a performance concern (i.e., your column values are/could
>> be vastly larger than your column names, and you need to query the
>> namespace before loading the values), then you might consider keeping
>> a separate column family which just contains the column names and
>> timestamps with empty values.
>>
>> On Sun, May 16, 2010 at 4:37 AM, David Boxenhorn <david@lookin2.com> 
>> wrote:
>>> Bill, I am a new user of Cassandra, so I've been following this 
>>> discussion
>>> with interest. I think the answer is "no", except for the brute force 
>>> method
>>> of looping through all your data. It's like asking for a list of all the
>>> files on your C: drive. The term "column" is very misleading, since
>>> "columns" are really leaves of a tree structure, not columns of a 
>>> tabular
>>> structure.
>>>
>>> Anybody want to tell me I'm wrong?
>>>
>>> BTW, Bill, I think we've corresponded before, here:
>>> http://www.dehora.net/journal/2004/04/whats_in_a_name.html
>>>
>>> On Fri, May 14, 2010 at 2:23 AM, Bill de hOra <bill@dehora.net> wrote:
>>>> A SlicePredicate/SliceRange can't exclude column values afaik.
>>>>
>>>> Bill
>>>>
>>>> Jonathan Shook wrote:
>>>>> get_slice
>>>>>
>>>>> see: http://wiki.apache.org/cassandra/API under get_slice and
>>>>> SlicePredicate
>>>>>
>>>>> On Thu, May 13, 2010 at 9:45 AM, Bill de hOra <bill@dehora.net>
wrote:
>>>>>> get_count returns the number of columns, not the names of those 
>>>>>> columns?
>>>>>> I
>>>>>> should have been specific, by "list the columns", I meant "list the
>>>>>> column
>>>>>> names".
>>>>>>
>>>>>> Bill
>>>>>>
>>>>>> Gary Dusbabek wrote:
>>>>>>> We have get_count at the thrift level.  You supply a predicate

>>>>>>> and it
>>>>>>> returns the number of columns that match.  There is also
>>>>>>> multi_get_count, which is the same operation against multiple
keys.
>>>>>>>
>>>>>>> Gary.
>>>>>>>
>>>>>>>
>>>>>>> On Thu, May 13, 2010 at 04:18, Bill de hOra <bill@dehora.net>
wrote:
>>>>>>>> Admin question - is there a way to list the columns for a

>>>>>>>> particular
>>>>>>>> key?
>>>>>>>>
>>>>>>>> Bill
>>>>>>>>
>>>
> 


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