On Fri, Mar 1, 2013 at 5:16 PM, Adam Venturella <aventurella@gmail.com> wrote:
My ColumnFamily is defined as follows:


CREATE TABLE UserProfileHistory(
    username text,
    timestamp bigint, -- millis since epoch
    data text, -- JSON
    PRIMARY KEY (username, timestamp)
) WITH CLUSTERING ORDER BY (timestamp DESC);


Each insert on the username adds to the wide row. The most recent profile history being able to be retrieved by 

SELECT * FROM UserProfileHistory WHERE username=:username LIMIT 1;

For some reporting needs I need to fetch the entire history, and I need to do it in ASC order instead of DESC.

One option is to do the sorting in code, collect N results, sort on the timestamps accordingly. Given the row is of N length, that could start to put an undo memory burden in my application layer, and I would like to avoid that if possible opting instead for Cassandra to perform the work.


So I am leaning towards this option:

2) min timestamp seek + ORDER BY

To start the process my initial timestamp would be 01-01-1970T12:00:00+0000 (assume that is in milliseconds, aka 0) I would then issue my query:

SELECT * FROM UserProfileHistory WHERE username=:username AND timestamp > :milliseconds ORDER BY timestamp ASC LIMIT 100

Once I have those initial results I would just pick my last timestamp from the result set and + 1 on it  and run the query again until I received 0 results.


The CQL works and returns my results as I expect. This will probably only be run once every 24 hours, maybe every 12 hours; point being, not often.

Am I setting myself up for a disaster down the line? 

No.

Paging over a partition key like you do in reverse order of the clustering order by is slightly slower than doing it in the clustering order, but not by a whole lot. It's slightly slower because 1) there will be backward seek underneath between the on-disk index block (not a huge deal) and 2) there is some reversing of lists going on before returning each query (again, not a huge deal). You'll be totally fine, especially if that query is not the one on which latency is the most critical.

--
Sylvain