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From vineet daniel <vineetdan...@gmail.com>
Subject Re: Data Modeling Conundrum
Date Sat, 08 May 2010 06:39:50 GMT
Query : Why are you sorting AFAIK cassandra sorts the keys by itself if you
are using ordered partitioning. And how do you store data pertaining to
single user but having several GUID's to attach with.


_______________________________________
Vineet Daniel
_______________________________________

Let your email find you....


On Sat, May 8, 2010 at 9:01 AM, William Ashley <washley@gmail.com> wrote:

> List,
> I have a case where visitors to a site are tracked via a persistent cookie
> containing a guid. This cookie is created and set when missing. Some of
> these visitors are logged in, meaning a userId may also be available. What
> I’m looking to do is have a way to associate each userId with all of the
> guids that it has been seen with. Conceptually, this would identify the
> unique (device, browser) pairs for each userId. The catch is that I want to
> be able to retrieve the most-recently-seen N guids for a userId.
>
>
> One possible solution to this problem in SQL looks like this (made up on
> the fly):
> # Table schema
> CREATE TABLE UserGuid ( userId INT, guid VARCHAR, when TIMESTAMP, PRIMARY
> KEY( userId, guid ), INDEX( userId, when ) );
>
> # For each request with guid G and userId U at time T
> INSERT INTO UserGuid ( userId, guid, when ) VALUES ( U, G, T ) ON DUPLICATE
> KEY UPDATE SET when = T;
>
> # To get most recent N guids for userId U
> SELECT guid FROM UserGuid WHERE userId = U ORDER BY when DESC LIMIT N;
>
>
> Hopefully I’ve sufficiently explained what I’m trying to do. Now on to
> solving this problem in Cassandra. I’ve been trying to find a way that
> allows both of the above operations to be performed efficiently. Updates are
> a breeze with a structure like this:
>
> // Row key is userId
> 12345 : {
>  // Column name is guid
>  ‘256fb890-5a4b-11df-a08a-0800200c9a66’ : {
>    // Column timestamp is last time guid was seen
>    timestamp : 387587235233
>  }
> }
>
> but getting the last N recently seen guids requires pulling all columns and
> sorting by timestamp. Retrievals can be done efficiently with a structure
> taking advantage of column sorting:
>
> // Row key is userId
> 12345 : {
>  // Column name is last time guid was seen
>  387587235233 : {
>    // Column value is guid
>    value: ‘256fb890-5a4b-11df-a08a-0800200c9a66’
>  }
> }
>
> where we use a slice get on the row with limit N (and reverse order).
> However, updates involve pulling all columns to de-duplicate guid values.
> Neither solution is ideal, and so I present this to you fine gentlemen who
> have more experience modeling data in Cassandra than I.
>
> I would much prefer to avoid any solutions that require pulling an
> indeterminate amount of data for either operation. For the time being I am
> using the first method and only pulling the first M columns, sorting, and
> taking the top N (M >= N).
>
> One thing I was thinking would be nice (if possible), is to have a column
> family where columns are either sorted by their timestamp, or by the time
> the column was created/updated (which may be equivalent to not sorting at
> all, but I have not looked at the implementation).
>
> I appreciate any feedback or suggestions you might have.
> - William
>
>

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