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 <ere...@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.br...@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 <ere...@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 >>> >> >> >
