[ndnSIM] do statistics about the lifetime of a content store entry in ndnSIM
Xiao yan Hu
xhbreezehu at gmail.com
Tue Dec 11 18:27:54 PST 2012
Hi Alex,
Thanks very much for the information you offered and it works :)
Sincerely,
Xiaoyan
On Tue, Dec 11, 2012 at 8:29 AM, Alex Afanasyev <
alexander.afanasyev at ucla.edu> wrote:
> Hi Xiaoyan,
>
> The "policy" that I was talking about is just a way to get access to the
> underlying data structure (insert/erase events).
>
> In any case, as it could be a generally useful metric, I decided to
> implement the necessary mechanics myself. If you're curious, you can
> check commit 8566f458f2aacc25f06683ce00219f7168ee71f5, in particular
> utils/trie/lifetime-stats-policy.h policy file.
>
> As of right now (commit f4a0359ac1dc60390ea41d8347c73a8c24a6789e) you can
> use the following code in order to get samples for lifetime of cached
> entries (copy from http://ndnsim.net/helpers.html#content-store):
>
> --------------------
> void
> CacheEntryRemoved (std::string context, Ptr<const ndn::cs::Entry> entry,
> Time lifetime)
> {
> std::cout << entry->GetName () << " " << lifetime.ToDouble (Time::S)
> << "s" << std::endl;
> }
> ...
> ndnHelper.SetContentStore ("ns3::ndn::cs::Stats::Lru", "MaxSize", "10000");
> ...
> ndnHelper.Install (nodes);
> // connect to lifetime trace
> Config::Connect ("/NodeList/*/$ns3::ndn::cs::Stats::Lru/WillRemoveEntry",
> MakeCallback (CacheEntryRemoved));
> --------------------
>
> I haven't had time, but you can write a tracer (similar to the one you
> already wrote for CacheHits/CacheMisses), which will make tracing totally
> trivial.
>
> Please note, that you *have to* use a specialized version of content store
> (ns3::ndn::cs::Stats::Lru, ns3::ndn::cs::Stats::Random, or
> ns3::ndn::cs::Stats::Fifo), and
> Config::Connect/Config::ConnectWithoutContext *have to* specify the correct
> content store implementation.
>
> Another note, for some replacement policies, entries may not be put in
> cache at all. In the current implementation, such entries will be reported
> with lifetime 0.
>
> ---
> Alex
>
> PS
> I have incorporated your implementation of the content store tracer
> (ndn::CsImpTracer). I also have added an example how to use the tracer (
> http://ndnsim.net/examples.html#level-binary-tree-with-content-store-trace-helper).
> Thanks again.
>
>
> On Dec 10, 2012, at 1:34 AM, Xiao yan Hu <xhbreezehu at gmail.com> wrote:
>
> > Hi Alex,
> >
> > Thanks very much for your information.
> > Actually I do not want to create a new replacement policy, but that
> updating the average lifetime of content store entries whenever cache
> replacement happens.
> > I found, e.g., in lru-policy.h, how an new content store entry is
> inserted as follow, and " base_.erase (&(*policy_container::begin ()));"
> shuld be for the replacement (&(*policy_container::begin ()) is the entry
> to replace), right?
> > 74 inline bool
> > 75 insert (typename parent_trie::iterator item)
> > 76 {
> > 77 if (max_size_ != 0 && policy_container::size () >= max_size_)
> > 78 {
> > 79 base_.erase (&(*policy_container::begin ()));
> > 80 }
> > 81
> > 82 policy_container::push_back (*item);
> > 83 return true;
> > 84 }
> >
> > I think I get stuck in that how to map &(*policy_container::begin ())
> into content store entry. Please forgive me about that I don't understand
> c++ very well.
> > And then I do not know what are eventually instantiated separately as
> "class Base, class Container, class Hook" of "template<class Base, class
> Container, class Hook>" in in lru-policy.h.
> > Would you pls give me a hint?
> >
> > Thanks,
> > Xiaoyan
> >
> > On Mon, Dec 10, 2012 at 4:28 PM, Alex Afanasyev <
> alexander.afanasyev at ucla.edu> wrote:
> > Hi Xiaoyan,
> >
> > Replacement and removal of content store entries in ndnSIM is controlled
> by so called policies. These policies are not really related specifically
> to the content store, but to the general data structure (trie-with-policy:
> utils/trie/trie-with-policy.h). There are currently three policies that
> are used in content stores: lru-policy.h, random-policy.h, and
> fifo-policy.h (code in utils/trie/ folder). If you create a new policy, a
> "new" content store can be created by adding a couple of lines (at least in
> the current code) into model/cs/content-store-impl.cc file:
> >
> > ---
> >
> > // (1) A little bit cheating to trick NS-3 object system
> >
> > template<>
> > TypeId
> > ContentStoreImpl< YOUR_POLICY >::GetTypeId ()
> > {
> > static TypeId tid = TypeId ("CONTENT_STORE_NAME") // e.g., to use in
> ndnStackHelper.SetContentStore ("CONTENT_STORE_NAME")
> > .SetGroupName ("Ndn")
> > .SetParent<ContentStore> ()
> > .AddConstructor< ContentStoreImpl< YOUR_POLICY > > ()
> > .AddAttribute ("MaxSize",
> > "Set maximum number of entries in ContentStore. If 0,
> limit is not enforced",
> > StringValue ("100"),
> > MakeUintegerAccessor (&ContentStoreImpl< YOUR_POLICY
> >::GetMaxSize,
> > &ContentStoreImpl< YOUR_POLICY
> >::SetMaxSize),
> > MakeUintegerChecker<uint32_t> ())
> > ;
> >
> > return tid;
> > }
> >
> > // (2) specialize content store implementation:
> >
> > template class ContentStoreImpl<lru_policy_traits>;
> >
> > ---
> >
> > Now regarding the policy itself.
> > For CS statistic generation I would recommend (at least for now)
> creating a custom "replacement" policy based on the existing one. That is,
> if you want stats for LRU policy, just copy lru-policy.h to
> lru-policy-stat.h and do necessary modifications. There is also
> multi-policy.h, which potentially could be a better fit (e.g., you would
> not need to "reimplement" stats for every replacement policy), but I
> haven't thoroughly tested this implementation.
> >
> > The code should be semi-self explanatory, though may be a little bit
> obscured. Looking forward to hear about your progress and/or problems :)
> >
> > Sincerely,
> > Alex
> >
> > On Dec 10, 2012, at 12:08 AM, Xiao yan Hu <xhbreezehu at gmail.com> wrote:
> >
> > > Hi all,
> > >
> > > Really happy to join the ndnSIM mailing list.
> > > Thank Alex very much for the development of ndnSIM which enables the
> simulation for NDN features.
> > > Hope everyone have fun with ndnSIM.
> > > I am doing some research on the NDN caching stuff and trying to
> simulate it with ndnSIM.
> > > I want to do statistics about the average time that an content object
> stays in the content store of a NDN node which is based on the lifetime of
> content store entries that have been replaced. Would you guys pls tell me
> where is the exact source code location of ndnSIM when an content store
> entry is replaced/erased?
> > > Look forward to hearing from your guys ：） Thanks in advance!
> > >
> > > Best regards,
> > > Xiaoyan
> >
> >
>
>
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