I have often thought of this.  Comments inline:

On 19 Jun 2013, at 13:44, William Burns <mudokonman@gmail.com> wrote:

All the L1 data for a DIST cache is stored in the same data container as the actual distributed data itself.  I wanted to propose breaking this out so there is a separate data container for the L1 cache as compared to the distributed data.

I thought of a few quick benefits/drawbacks:

Benefits:
1. L1 cache can be separately tuned - L1 maxEntries for example
2. L1 values will not cause eviction of real data
3. Would make https://issues.jboss.org/browse/ISPN-3229 an easy fix
4. Could add a new DataContainer implementation specific to L1 with additional optimizations
5. Help with some concurrency issues with L1 without requiring wider locking (such as locking a key for an entire ClusteredGet rpc call) - https://issues.jboss.org/browse/ISPN-3197.

Drawbacks:
1. Would require, depending on configuration, an additional thread for eviction

Not really - the same eviction thread used for the main data container could also clean things up in the L1 DC.

2. Users upgrading could have double memory used up due to 2 data containers

This is just a fixed (and small) overhead.  Not actually double the memory used by the entire grid.

Additional drawbacks:
- More complex lookups in the DC.  Code that would otherwise just call DC.get() would now need to also check L1DC.  This would be scattered all over the code-base - unless perhaps the main DC would implicitly also check the contents of the L1DC (if one is available).


Both?:
1. Additional configuration available
   a. Add maxEntires just like the normal data container (use data container size if not configured?)
   b. Eviction wakeup timer?  We could just reuse the task cleanup frequency?
   c. Eviction strategy?  I would think the default data container's would be sufficient.

I was wondering what you guys thought.

Thanks,

 - Will
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Manik Surtani

Platform Architect, JBoss Data Grid