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From Bill de hOra <b...@dehora.net>
Subject Re: list of columns
Date Mon, 17 May 2010 08:59:48 GMT
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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