[chord] 【chord】questions about Chord code

[Emil Sit]

On Mon, 28 April 2008 at 00:03 (+0800), 潘凯 wrote:
> the first three lists(locs,cachedlocs,loclist) point to the same locwraps.Why
> design three different data structures to record the same information?Is it
> because different data structures have different advantages in the search
> operation? 

Yes, exactly.

> introduction on the function of the following data members,can you
> tell me to what consideration you designed them: 
>     float a_var_;

The STP communication protocol uses the latency and stddev/variance
per RPC to determine the appropriate timeout to detect lost packets.
See http://pdos.csail.mit.edu/papers/dhash:nsdi/index.html
for more information.

>     unsigned long nrpc_;
>     //is it a rpc counter?why count the  rpctimes? for replace the location?

Yes, it is just a count of the number of RPCs for statistics purposes.

>     time_t knownup_;
>     time_t age_;
>     int32_t budget_;

These fields were introduced as part of the implementation of Accordion.
The knownup field specifies (I believe) how long the node has been
online, age allows each node to distinguish if information that it
receives about a remote node is older than what information it already
has, and the budget indicates the bandwidth budget of that node for
routing table maintenance (used only with -m accordion).

http://pdos.csail.mit.edu/papers/accordion:nsdi05/index.html

Hope this is helpful.

-- 
Emil Sit / MIT CSAIL PDOS / http://pdos.csail.mit.edu/chord/