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    <p>Columns within a row are always sorted by name with the given comparator. You cannot sort by timestamp or value or anything else, or Cassandra would not be able to merge multiple updates to the same column correctly.</p> <p>As to your use case, I can think of two options.</p> <p>The most similar to what you are doing now would be to create a second columnfamily, ThreadMostRecentPosts, with timeuuid columns (you said "keys" but it sounds like you mean "columns"). When a new post arrives, delete the old most-recent column and add a new one.</p> <p>This has two problems:</p> <ul> <li>The unit of replication is the row, so having this grow indefinitely could be problematic. (Using <a href="http://www.datastax.com/dev/blog/whats-new-cassandra-07-expiring-columns">expiring columns</a> to age out no-longer-relevant thread information might help.)</li> <li>You need a lock manager so that multiple posts to the same thread don't race and possibly leave multiple entries in this row.</li> </ul> <p>I would suggest instead creating a row per day (for instance), whose columns are the thread IDs and whose values are the most recent post. Adding a new post just updates the value in that column; no delete/re-add is done, so the race is not a problem anymore. You don't get sorting for free anymore but that's okay because you're limiting it to a small enough set that you can do that sort in memory (say, yesterday's threads and today's).</p> <p>(Finally, I would add that I can say from experience that having a cutoff past which old threads don't get bumped to the front by a new reply is a Good Thing.)</p>
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    1. POCan you sort a GET on a Cassandra column family by the Timestamp value created for each column entry, rather than the column Keys?
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    1. USjbellis
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    1. COYes firstly I do mean columns not keys... well the column 'keys' anyways. I don't know admitantly the idea would be that only 20 or so threads would be active for each board anyways but I'm not sure how clean your solution would be, i'm also worried about the idea of multiple access as inserting and deleting could mean that a get request happens inbetween making the data invalid.
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      1. USPeter Fox
    2. COHence my caution that you'd need a lock manager for the first solution. The second is inherently concurrency-safe.
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    3. CO@jbellis: I think Cassandra should provide a configurable option on per column family basis to do columns sorting by time-stamp rather than column names. However this _doesn't_ mean to say that there wont be any column names. This would be really helpful to maintain time-sorted columns without keeping time-stamps in column names space which might otherwise be used to store more relevant column names useful for retrievals. Very frequently we need to store data sorted in time order. Therefore I think this may be a very general requirement & not specific to just his & my use-case alone.
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      1. USRajat Gupta
 

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