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Morten Jorgensen commented on CASSANDRA-2469:
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There are other valid reasons why you would want the TTL on the key/row rather
than the individual columns. The reason why you store your data as columns
under a common key is that the data is related, and hence you want to ensure
that all data exists as long as the key exists. Example:
I have developed a plugin for Tomcat that stores user session data in
Cassandra, effectively making Tomcat stateless (and scalable) even if it
maintains user sessions. Session data is stored in Cassandra under the session
ID (key/row), as session attribute name/value-pairs (columns). Sessions time
out after N minutes of inactivity, and I would prefer to use Cassandra's TTL
for this. Otherwise I have to traverse all sessions periodically and purge
sessions that are past their expiry time. But, the problem using the
column-level TTL is that I risk timing out only parts of a user session, rather
than all of it. So, a user that accesses JSPs that require read/write access to
only certain session objects will retain those objects in Cassandra, while
other session objects will expire with their respective column TTL's. This
creates an inconsistent session, with some data expiring and some data
remaining in the session - while what I need is the entire session to remain or
expire as a whole.
This is one valid use case for key-level TTL, and this is only one specific
example of the more general use case of column consistency. I suggest that this
issue is re-opened an re-evaluated from this perspective.
> TTL on rows
> -----------
>
> Key: CASSANDRA-2469
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2469
> Project: Cassandra
> Issue Type: New Feature
> Components: Tools
> Affects Versions: 0.7.4
> Reporter: Patrick Julien
> Priority: Minor
>
> It's currently possible to achieve this by setting a TTL on every column
> found in the row. However, in some scenarios, that requires too much
> storage. A TTL on the row itself would be a more concise and space efficient
> way of doing this.
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