swarm/network: Revised depth and health for Kademlia #1051

nolash · 2018-12-12T12:29:10Z

The contents of this PR are:

A stricter definition of kademlia depth.
An adapted definition of health, with corresponding changes to the related methods.
Moving health-related methods to PeerPot as receiver.
Reactivate tests that were skipped because of health problems.

1. Depth

For your pleasure we attempt both a formal definition and a definition legible for puny humans.

Humans:

Proximity order - po - is a metric of distance between two peer addresses. You obtain the numerical value of po by:

Performing XOR on the two addresses
Count the number of leading bits in the result, from left to right.

In terms of depth, deeper means higher numeric po value, and shallower means lower numeric po value.

When a peer is deeper it is also closer.

Your neighbors are your closest peers

The depth is the whichever is shallower of:

the shallowest bin that is empty
the bin of the shallowest of your neighbors

To find your neighbors:

Identify the MinProxBinSize number of your deepest peers.
Identify the shallowest bin of those peers.
Your neighbors are all the peers in that bin and deeper.

(the name MinProxBinSize should probably change to NeighbourhoodSize, but let's not get ahead of ourselves)

Formal: (pending review)

depth d such that for every i < d, |{p, PO(p) = i }|>= 1 and |{p, PO(p) >= d}|>=MinProxBinSize

2. Health

The full parameter has been removed both from the PeerPot and as a condition of health in the test code. This is because the evaluating whether a kademlia was "full" involved allowing empty bins shallower than the depth. With the new definition of depth, this cannot occur.

Thus, currently the only condition for a healthy node is if the node is connected to the neighbours it should be connected to. "Should have" means that we know of all the nodes in the network, and thus can tell which ones are the closest of all of them and thus that the node should be connected to them.

Saturation has been added as a property of the PeerPot object.

The "got" ("which peers do I have") and "missing" ("who peers should I have had but don't") results are also added to the knowNeighbours (prev: knowNearestNeighbours) method, to conform with the connectedNeighbours (prev: gotNearestNeighbours) method.

3. Move test methods

The methods knowNeighbours, connectedNeighbours and Healthy now have PeerPot as receiver. PeerPot extends Kademlia. The reasoning for this is as follows:

Methods involving PeerPot are dependent on kademlia, and instantiation of PeerPot depends on a kademlia parameter. By reversing the relationship, fewer arguments are needed when calling the methods. In general, it seems to simplify the code.

Previously a MinProxBinSize parameter was being passed to the health functions externally. In every case this was the same as the hardcoded MinProxBinSize value in the default kademlia params. It is assumed that the value never will be anything else, and if it is, it should anyway be the same value as the PeerPot was created with.

Furthermore, health-related methods are only used in tests, and should be concealed from production code. Moving the methods from the Kademlia object to the PeerPot object serves as preparation for this.

4. Test reactivation

Currently the following tests are failing:

~~in swarm/network/kademlia_test.go: TestSuggestPeerFindPeers~~ skipped
tests in swarm/network/simulations/discovery/

Furthermore, tests auditing depth and healthy should be revised the make sure they test the new definitions correctly. These include:

TestKademliaCase* deferred to swarm/network: Add tests for complex connectivity evaluations #1069
Test health evaluations
~~Test saturation evaluations~~ deferred to swarm/network: Add tests for complex connectivity evaluations #1069

nolash · 2018-12-17T14:50:48Z

The SuggestPeersFindPeers test will be skipped for this PR, but will be fixed in immediately following PR. #1063

zelig

WaitTillHealthy changes should be in another separate PR I think.
ready to submit after linter error fixed https://travis-ci.org/ethersphere/go-ethereum/jobs/469257146#L513

zelig · 2018-12-18T06:41:16Z

swarm/network/kademlia.go

+	KnowNN         bool     // whether node knows all its nearest neighbours
+	CountKnowNN    int      // amount of nearest neighbors connected to
+	CulpritsKnowNN [][]byte // which known NNs are missing
+	GotNN          bool     // whether node is connected to all its nearest neighbours


maybe we should rename these fields to connected too?

This terminology of Got and Culprits is not clear to me

nolash · 2018-12-18T09:05:36Z

@zelig I disagree, I'm afraid. The only change made to the Simulation is a parameter that let's you specify a minproxbinsize that may even be different from the ones the kademlias in the simulation has. I think this is highly relevant to depth correctness.

swarm/network/kademlia.go

holisticode · 2018-12-19T18:41:29Z

swarm/network/kademlia.go

-// It is used in Healthy function for testing only
-func (k *Kademlia) saturation(n int) int {
+// saturation iterates through all peers and
+// returns the smallest po value in which the node has less than n peers


what is n peers? There is no n in this function? Is n == k.MinBinSize?

Saturation is treated in next PR. Let's clarify it there. (even if I actually changed the comment here)

swarm/network/kademlia.go

holisticode · 2018-12-19T18:49:34Z

swarm/network/kademlia.go

+	KnowNN         bool     // whether node knows all its nearest neighbours
+	CountKnowNN    int      // amount of nearest neighbors connected to
+	CulpritsKnowNN [][]byte // which known NNs are missing
+	GotNN          bool     // whether node is connected to all its nearest neighbours


This terminology of Got and Culprits is not clear to me

holisticode · 2018-12-19T18:54:03Z

swarm/network/kademlia_test.go

@@ -186,72 +290,98 @@ func TestSuggestPeerBug(t *testing.T) {
 }

 func TestSuggestPeerFindPeers(t *testing.T) {
+	t.Skip("The SuggestPeers implementation seems to have weaknesses exposed by the change in the new depth calculation. The results are no longer predictable")
+


Hang on - we introduce a change here which breaks a test and we simply skip the test? Is that healthy :) ?

When we fix from the ground up we will inevitably break things further up. In the interest of keeping deltas small between PRs, it is skipped. Fixing it is not necessarily trivial.

Anyway see comment from @zelig below:

You can still submit separate on ethersphere but on upstream lets not do this.

swarm/network/kademlia_test.go

swarm/network/simulations/discovery/discovery_test.go

swarm/pss/api.go

holisticode

Great job, I am happy to see things clearing up with everything related to kademlia.

I am mostly requesting some clarification of some comments

zelig

Now it needs a rebase since at least javier's PR is merged in.

zelig · 2018-12-19T21:15:43Z

swarm/network/kademlia.go

@@ -388,6 +390,7 @@ func (k *Kademlia) EachBin(base []byte, pof pot.Pof, o int, eachBinFunc func(con
 // EachConn is an iterator with args (base, po, f) applies f to each live peer
 // that has proximity order po or less as measured from the base
 // if base is nil, kademlia base address is used
+// It returns peers in order deepest to shallowest


I am not 100% this terminology is the right one. It is apparent in this context.
Maybe in the context of a kademlia table the container represents a view of the network from the point of view of the node. With the queen of the hive sitting in deep inside, we can talk about proximity orders in terms of deep and shallow. But if the pivot is another peer it is strange to say you iterate our hive from deep to shallow. It is just best to say from closest to farthest from the pivot or DECENDING PROXIMITY

It is just best to say from closest to farthest from the pivot or DECENDING PROXIMITY

The main objective of introducing this terminology is both to simplify and disambiguate. In the spirit of the former, I don't think the quote above serves the purpose.

If the term depth can't serve both purposes, then let's use two terms.

zelig · 2018-12-19T21:17:23Z

swarm/network/kademlia.go

+	// iterate through nearest neighbors in the peerpot map
+	// if we can't find the neighbor in the map we created above
+	// then we don't know all our neighbors
+	// (which sadly is all too common in modern society)


swarm/network/kademlia.go

Pending add test for saturation And add test for as many as possible up to saturation

zelig · 2018-12-22T08:13:50Z

merged as ethereum/go-ethereum#18354

nolash added enhancement stability labels Dec 12, 2018

nolash assigned zelig and nolash Dec 12, 2018

nolash added the in progress label Dec 12, 2018

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nolash requested review from holisticode, janos, acud and zelig as code owners December 14, 2018 11:56

nolash changed the title ~~swarm/network: Revised depth calculation for Kademlia~~ swarm/network: Revised depth and health for Kademlia Dec 14, 2018

nolash force-pushed the depth-the-next-generation branch from 7faa5ec to 5fc0130 Compare December 17, 2018 14:39

nolash requested a review from nonsense as a code owner December 17, 2018 16:18

zelig approved these changes Dec 18, 2018

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zelig added this to the 2018 Christmas Edition milestone Dec 18, 2018

zelig mentioned this pull request Dec 18, 2018

kademlia, connectivity, stability -- meta #1068

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nolash mentioned this pull request Dec 18, 2018

swarm/network: Add tests for complex connectivity evaluations #1069

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nolash added ready for review and removed in progress labels Dec 18, 2018

nolash force-pushed the depth-the-next-generation branch 2 times, most recently from b5a31b9 to 0ecd873 Compare December 19, 2018 10:43

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nolash added 22 commits December 21, 2018 16:43

swarm/network: Remove commented out code

957c8cc

swarm/network: Rename health test functions

af9b98c

swarm/network: Too many n's

5bf8307

swarm/network: Change hive Healthy func to accept addresses

166f084

swarm/network: Add Healthy proxy method for api in hive

e41cf54

swarm/network: Skip failing test out of scope for PR

13a0e6a

swarm/network: Skip all tests dependent on SuggestPeers

31807b2

swarm/network: Remove commented code and useless kad Pof member

e665380

swarm/network: Remove more unused code, add counter on depth test errors

2990503

swarm/network: WIP Create Healthy assertion tests

cbf6d77

swarm/network: Roll back health related methods receiver change

eec6ba7

swarm/network: Hardwire network minproxbinsize in swarm sim

89e7259

swarm/network: Rework Health test to strict

bdcca4c

Pending add test for saturation And add test for as many as possible up to saturation

swarm/network: Skip discovery tests (dependent on SuggestPeer)

f5b6fd9

swarm/network: Remove useless minProxBinSize in stream

f295834

swarm/network: Remove unnecessary testing.T param to assert health

6a815a9

swarm/network: Implement t.Helper() in checkHealth

78905f5

swarm/network: Rename check back to assert now that we have helper magic

a5953f6

swarm/network: Revert WaitTillHealthy change (deferred to nxt PR)

89ea2fe

swarm/network: Kademlia tests GotNN => ConnectNN

04a3cff

swarm/network: Renames and comments

d45b0c4

swarm/network: Add comments

412b02f

nolash force-pushed the depth-the-next-generation branch from 2740f77 to 412b02f Compare December 21, 2018 15:44

zelig approved these changes Dec 21, 2018

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zelig added the ready to submit to ethereum/go-ethereum label Dec 21, 2018

zelig closed this Dec 22, 2018

nolash mentioned this pull request Jan 14, 2019

swarm/network: Add tests for complex connectivity evaluations (2) #1108

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frncmx deleted the depth-the-next-generation branch January 22, 2019 09:33

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swarm/network: Revised depth and health for Kademlia #1051

swarm/network: Revised depth and health for Kademlia #1051

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swarm/network: Revised depth and health for Kademlia #1051

swarm/network: Revised depth and health for Kademlia #1051

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nolash commented Dec 12, 2018 • edited Loading

1. Depth

2. Health

3. Move test methods

4. Test reactivation

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zelig commented Dec 22, 2018

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