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From Benjamin Black...@b3k.us>
Subject Re: Model Question
Date Thu, 25 Mar 2010 16:56:40 GMT
Erez,

To make this work you have to make your model fit Cassandra, not the
other way around.  As a rule, you either do complex queries via client
code to process the results of several, simpler queries or via a CF
you create to act as an index.  Yes, this means you have to write data
to each index in which it belongs.  Which approach to use depends
entirely on your application and your preferences.


b

On Thu, Mar 25, 2010 at 2:09 AM, Erez Efrati <erezef@gmail.com> wrote:
> You are correct Chris.
> I am a newbie too in this field.
> I like the Cassandra/NoSQL way and I am trying to see if it can fit my
> model.
> Thanks,
> Erez
>
> On Thu, Mar 25, 2010 at 11:03 AM, Christopher Brind
> <christopher.brind@googlemail.com> wrote:
>>
>> Hi,
>> I wondered if you were eluding to something more complex.   You'd probably
>> want to create a index using something along the lines that Peter suggested.
>> :)
>> But I'm a Cassandra / Column DB newbie, so my experience ends just about
>> ... here. :)
>> Cheers,
>> Chris
>>
>> On 25 March 2010 08:59, Erez Efrati <erezef@gmail.com> wrote:
>>>
>>> Hi Chris,
>>> So, if I get it right, you suggest that I pull all the columns for in a
>>> single row and do the sorting client side?
>>> The user-friends-messages was just an example and maybe not the best I
>>> could come up with cause I agree that there are not too many friends in
>>> general that send you messages.
>>> What I wanted to keep track of companies and user-visit count. Each
>>> company can have potentially millions of users. Then for each company I want
>>> to display in pages from the top visiting user to the least one.
>>> Would you still upload the whole company row columns and sort it on the
>>> client?
>>> How do keep updating the visits?
>>> Thanks,
>>> Erez
>>> On Thu, Mar 25, 2010 at 12:35 AM, Christopher Brind
>>> <christopher.brind@googlemail.com> wrote:
>>>>
>>>> Hi Erez,
>>>> Don't know how many friends a user in your system is likely to have, but
>>>> are they likely to have received so many messages from friends that you
>>>> can't sort it in your client app?
>>>> See:
>>>>
>>>> http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collections.html#sort(java.util.List)
>>>> Assuming the user has 10,000 friends (I'm sure I don't even know 10,000
>>>> people :) with Java's Collections.sort which guarantees performance of O(n
>>>> log(n)) let's say it takes 1ms to process each item, you're looking at
>>>> 40,000ms to do a sort plus a little overhead to avoid the O( n2 log(n))  -
>>>> that's 40 seconds to sort for 10,000 friends...
>>>> On Facebook I have 363 friends that's 929ms + overhead, i.e. around a
>>>> second.  Apparently the average Facebook user has 130 friends:
>>>> http://www.facebook.com/press/info.php?statistics
>>>> So I can't imagine the sort exceeding much more than a second or so
>>>> except for the most popular users - in practice I would hope sub-second
>>>> easily.  Does that help?  Or is there something special happening in your
>>>> system?
>>>> Cheers,
>>>> Chris
>>>>
>>>>
>>>> On 24 March 2010 20:36, Erez Efrati <erezef@gmail.com> wrote:
>>>>>
>>>>> Hi,
>>>>> I can't figure out how to use model the following using column family
>>>>> and the way the columns are sorted (by their name).
>>>>> Lets say I have a list of users and for each user I wish to display a
>>>>> list of all the friends he has ordered by the number of messages they
sent
>>>>> him so far (desc from most to least).
>>>>> I can't see how this is going to work since the columns sorting is
>>>>> always by the name of the column and not its value. I thought of having
a
>>>>> row for each user and the columns will be the friends that email him.
But
>>>>> the column name needs to be the number of messages to be sorted and the
>>>>> value will be the friend's user ID. But then, when a friend is sending
a
>>>>> message to another user how do I increment his count of message he sent
so
>>>>> far to that user?
>>>>> How can I model this with Cassandra? Is it possible?
>>>>> Thanks in advance,
>>>>> Erez Efrati
>>>
>>
>
>

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