re: [RRG] cache issues in LISP and CONS

[Scott Brim <swb@employees.org>]

On 18 Oct 2007 at 11:11 -0400, Noel Chiappa allegedly wrote:
>     > From: Xu Xiaohu <xuxh@huawei.com>
> 
>     > How to determine the widely used destination
> 
> I spent a lot of time thinking about that, and finally came up with what I
> think is a very efficient (in terms of overhead), and extremely effective (in
> terms of correctly identifying which mappings are widely used) system for
> deciding which entries to cache in the CDRs.
> 
> Basically, it works by starting with the actual mappings in the
> aCARs; those entries have to always exist anyway, so it is just an
> extra field in those entries, which gets incremented any time the
> mapping is requested. When the aCARs notice a lot of requests for a
> particular mapping, they suggest to their parent CDR(s) that they
> cache that mapping. The same process then repeats at each CDR level.

If it is just about request rate, then I see no reason for the aCAR to
inform its upstream nodes of anything.  Its upstream nodes are already
quite aware of how many requests are being made for various prefixes,
and the aCAR is not aware of conditions under which the CDR is
operating.  I don't think it's good to design in interdependency when
an individual CDR has all the information the aCAR could give it, plus
more that the aCAR does not know about.  A cache system will cause
frequently requested information to be present in the intermediate
nodes.  It's simple and it doesn't depend on control exchanges.  

On the other hand, Vince pointed out that communication between an
aCAR and its immediate upstream CDR could be used to communicate "high
load experienced", and affect which aCARs the CDR [cluster] sends
requests to. 

Scott

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