[infinispan-issues] [JBoss JIRA] (ISPN-4132) Group-based eviction

[Paul Ferraro (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-4132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12959336#comment-12959336 ] 

Paul Ferraro edited comment on ISPN-4132 at 4/4/14 10:35 AM:
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I disagree.  The likelihood that a given session attribute will be accessed is not independent of, but is correlated with, the access recency of the session with which it is associated.  If a session was not accessed for a given period then we know for certain that its attributes were not accessed for at least as long.

The greater point I was trying to make is: it's not always meaningful to base eviction off of a maximum number of entries.  WildFly can be configured to store sessions as either 2 entries per session (the default), or N+1 entries per session, where N is the number of attributes in the session.  In both cases, all cache entries associated with a session make up a single group.  As a user/administrator, I am more interested in specifying the maximum number of sessions (i.e. groups) to keep in memory - irrespective of the cache entry mapping implementation details, since the effective value of max-entries would differ based on the session mapping strategy.
                
      was (Author: pferraro):
    I disagree.  The likelihood that a given session attribute will be accessed is not independent of, but is correlated with, the access recency of the session with which it is associated.  If a session was not accessed for a given period then we know for certain that its attributes were not accessed for at least as long.

The greater point I was trying to make is: it's not always meaningful to base eviction off of a maximum number of entries.  WildFly can be configured to store sessions as either 2 entries per session (the default), or N+1 entries per session, where N is the number of attributes in the session.  In both cases, all cache entries associated with a session make up a single group.  As a user/administrator, I am more interested in specifying the maximum number of sessions to keep in memory - irrespective of the cache entry mapping implementation details, since the effective value of max-entries would differ based on the session mapping strategy.
                  
> Group-based eviction
> --------------------
>
>                 Key: ISPN-4132
>                 URL: https://issues.jboss.org/browse/ISPN-4132
>             Project: Infinispan
>          Issue Type: Feature Request
>          Components: Eviction
>    Affects Versions: 6.0.2.Final
>            Reporter: Paul Ferraro
>            Assignee: Dan Berindei
>
> Currently, Infinispan only supports size-based eviction.   We can configure a cache with a specific max-entries, so if the size exceeds this value infinispan will evict any surplus entries.
> However, if the cache has grouping enabled, it is perhaps more useful to use group-based eviction.  In this scenario, max-entries would be interpreted as "max-groups", and infinispan would evict entire groups of cache entries if the number of groups exceeds this value.
> In WildFly, web sessions make use of grouping.  A single web session will map to a single group of multiple cache entries, where the number of entries is not necessarily the same for a given session.  In this case, evicting per cache entry does not make sense - all entries of a session should be evicted or not at all.  Also, users can specify the max number of sessions they want to remain in memory.  Until infinispan supports group-based eviction, translating this value to an appropriate max-entries is cumbersome and imprecise.

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