[chord] Analysing Packets

[Emil Sit]

On Fri, 18 April 2008 at 00:10 (+0100), Brown, Adam J wrote:
> place.  The thing is, for a large majority of the packets (>95%) it
> states "UDP Checksum Incorrect".  Why is this?

Make sure you are capturing the entire packet off the wire.
If Wireshark is like tcpdump, it may only capture the first 68 bytes of
each packet.  This setting may be called the snaplen.

> I was also wondering what the output from the dbm store and fetch
> operations mean?  Here is an example:
> store:
> 97bb / 3 / 5eff 967c a96b

This comes from harness_t::storecb:

    s << (i->key>>144) << " / " << (getusec () - start)/1000 << " /";
    for (size_t j = 0; j < i->path.size (); j++)
      s << " " << (i->path[j]>>144);
    s << "\n";

i.e., the top 16 bits of the key stored, the number of ms for the store,
and then the top 16 bits of each node in the insertion path.
 
> fetch:
> 1ff7 3 / 1 2 / 2 0 0 1aea 1e51 / 0

harness_t::fetchcb:

    buf << (IDs[i]>>144) << " " << (getusec () - start)/1000 << " /";
    for (u_int i = 0; i < blk->times.size (); i++)
      buf << " " << blk->times[i];
    buf << " /";

    buf << " " << blk->hops << " " <<  blk->errors
        << " " << blk->retries;
    for (u_int i=0; i < path.size (); i++) {
      buf << " " << (path[i]>>144);
    }
    buf << " / " << blk->expiration;

The key id, the e2e fetch time, time for lookup vs time for fetch,
hops, errors, retries, the path and then the expiration time.
 
> And one other thing, how do you kill a node from the terminal?  I have been
> unable to find the command to do so.

Just kill the start-dhash process.

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