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From Lawrence Turcotte <lawrence.turco...@gmail.com>
Subject DESIGN QUESTION: Need to update only older data in cassandra
Date Sat, 16 Nov 2013 19:45:47 GMT
that is, data consists of of an account id with a timestamp column that
indicates when the account was updated. This is not to be confused with row
insertion/update times tamp maintained by Cassandra for conflict resolution
within the Cassanda Nodes. Furthermore the account has about 200 columns
and updates occur nightly in batch mode where roughly 300-400 million
updates are sent. The problems occurs during the day where updates can be
sent that possibly contain older data then the nightly batch update. As
such the requirement to first look at the account update time stamp in the
database and comparing the proposed update time stamp to determine whether
to update or not.

The idea here is that a read before update in Cassandra is generally not a
good idea. To alleviate this problem I was thinking of either maintaining a
separate Cassandra db with only two columns of account id and update time
stamp and using this as a look up before updating or setting a stored
procedure within the main database to do the read and update if the data
within the database is older.

UPDATE Account SET some columns WHERE lastUpdateTimeStamp <
proposedUpdateTimeStamp.

I am kind of leaning towards the separate database or keys pace as a simple
look up to determine whether to update the data in the main Cassandra
database, that is the database that contain the 200 columns of account
data. If this is the best choice then I would like to explore the pros and
cons of creating a separate Cassandra Node cluster for look up of account
update time stamps vs just adding another key space within the main
Cassandra database in terms of performance implications. In this account
and time stamp only database I would need to also update the time stamp
when the main database would be updated.

Any thoughts are welcome

Lawrence

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