From: =?iso-8859-1?Q?Michael_Gr=F8nager?= <gronager@ceptacle.com>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: quoted-printable
Date: Thu, 29 Dec 2011 23:05:55 +0100
Message-Id: <AB205206-AC96-4A95-B100-E8F4461B08C5@ceptacle.com>
To: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Mime-Version: 1.0 (Apple Message framework v1251.1)
Subject: [Bitcoin-development] Trickle in CNode::SendMessages
Precedence: list

In CNode::SendMessages there is a trickle algorithm. Judging from the =
comments it is supposed to:

* at each update round a new (random) trickle node is chosen, with 120 =
nodes and an average round time of 100ms (the sleep) we will have moved =
through roughly all nodes every 12-15 seconds.
* when a node is the trickle node it will get to send all its pending =
addresses to its corresponding peer.
* when a node is not trickle node (the rest of the nodes) we send =
transaction-invs, however, only 1/4 of them - the rest is pushed to wait =
for the next round and would eventually get sent.

However, the way the 1/4 of the invs are chosen is by:=20
	(inv.getHash() ^ hashSalt) & 3 =3D=3D 0

As hashSalt is a constant (static, generated on start up) and as the =
hash of an inv is constant for the inv too, the other 3/4 will never get =
sent and hence it does not make sense to carry them around from round to =
round:
	if (fTrickleWait) vInvWait.push_back(inv);=20
and:
	pto->vInventoryToSend =3D vInvWait;

The hashSalt will be different for each node in the peer-to-peer network =
and hence as long as we have much more than 4 nodes all tx'es will be =
sent around.

Ironically, this (wrong?) implementation divides the inv forwarding hash =
space into 4, along the same lines as we discussed last week for DHTs...

I suggest to either keep the algorithm as is, but remove the redundant =
vInvWait stuff, or to change the algorithm to e.g. push the tx'es into a =
multimap (invHash^hashSalt, invHash) and choose the first 25% in each =
round.=20

The last alternative is that I have misunderstood the code... - if so =
please correct me ;)

Happy New Year!

Michael