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Morten Jorgensen commented on CASSANDRA-7534:
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Robert, thanks a lot for your comment. This explains the negative impact of
doing what I am trying to do. Each access to a web session would require the
TTL to be updated, regardless of if the actual session data changes or not.
This again means that I do indeed hit the anti-pattern in Aleksey's article.
I do _not_ want to store session data in memory in Tomcat, as this forces me to
use a sticky load balancer. I want any request to be able to hit any Tomcat
node, and let tomcat be completely stateless and horizontally scalable. If this
means that I need to run periodical purge-scripts across my sessions in
Cassandra then so be it.
> TTL on rows to ensure data consistency
> --------------------------------------
>
> Key: CASSANDRA-7534
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7534
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Morten Jorgensen
> Fix For: 3.0
>
>
> Requesting TTL on key/row-level to ensure consistency between data stored in
> columns under the same key. Please refer to original request for this
> enhancement in CASSANDRA-2469.
> There are 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.
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