vlc.md

Clock & p2p combined or optimizing

This document is used to discuss how clock or vlc can be combined or optimized with p2p protocols.

Modeling & Data Structure

Simple Modeling

Suppose there were n nodes in cohort network, n is three in below graph. It looks like below, when start node running.

gitGraph
   commit tag: "1, 0, 0"
   commit tag: "2, 0, 0"
   branch B
   branch C
   commit tag: "2, 0, 1"
   
   checkout B
   commit tag: "2, 1, 0"
   commit tag: "2, 2, 0"
   
   checkout main
   merge B
   commit tag: "3, 2, 0"

   checkout C
   merge B
   commit tag: "2, 2, 2"
   commit tag: "2, 2, 3"
   
   checkout main
   merge C
   commit tag: "4, 2, 3"
   

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Data Structure

• Purpose
  • Display clock’s state & change in global view.
• Related data structure as below:
  • Message (Ref P2P Design) or Transaction
    • VLC: Verifiable logical clock
    • node_id
  • MergeLog as edge, ClockInfo as vertex.
    • main data structure for db saving and recovering the dag propagation graph about clocks.

classDiagram
    note for Message "Message or tx in network"
    note for MergeLog "Merging log save to db, as the edge"
    note for ClockInfo "ClockInfo save to db, as the vertex"
    
    Message <-- Clock
    MergeLog
    ClockInfo <-- Clock
    Message: +vlc Clock
    Message: +isZK bool
    Message: +from/toAddr str
    Message: +signature str
    
    Clock: -value map（id, u128）
    class Clock {
	    -partial_cmp()
	    -inc()
	    -merge()
    }
    
    class ClockInfo {
	    -nodeID u128
	    -eventCount u128
	    -createAt u128
	    -Clock Clock
	    -messageId String
    }
    
    class MergeLog {
	    -fromID u128
	    -toID u128
	    -startCount u128
	    -endCount u128
	    -startClockHash ClockHash
	    -afterClockHash ClockHash
	    -mergeAt u128
	    +serialize()
	    +deserialize()
    }
    

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Persistence & DB

Clock data save to the KV db, LMDB for persistence for now.

Maybe the postgreDB or influxDB is a better choice for next step.

• ClockInfo
  • key: nodeid-count-vertex, value: serde(ClockInfo)
• MergeLog
  • key: fromid-fcount-toid-tcount-edge, value: serde(MergeLog)
• CurCount, not must
  • key: nodeid, value: current_count
• When needs to rebuild the dag of clock propagation,
  • first use ClockInfo node to construct participant event line,
  • then use MergeLog info for constructing the edge of the dag.

State Increment Sync & Separate Clock

Separate State & Clock

Because global data state is much big, so can’t gossip to other participants with so big data package. Separate full state and clock is must to do.

• But clock needs to reference transactions or message.
  • So message_id needs add to ClockInfo.

State Increment Sync

There are two methods for state increment sync, make events organize to merkle tree or just the native vlc structure.

• 1、Event merkle tree
  • Transactions merkle tree in block header, just for light client quick verify.
    • whether there is a transaction block in our design ? not must
  • World state MPT or merkle tree in memory
    • whether there is a world state tree in our design ?
      • Must be consensus algorithm & full transaction order. not must
      • if not, it will cause state not consistency.

So, we accept second method, just use native vlc structure to sync state directly.

• 2、direct sync by vlc
  • first sync clock, then active pull diff events.
  • init setup, pull from many peers neighbor by needs in parallel.

sequenceDiagram
	  
    A->>B: Event A-1 happen, send latest C_A
    alt if C_A>C_B 
        B->>A: req diff of C_A minus C_B
        A->>B: send [ clocks of C_A - C_B]
    else if C_A<C_B
        B->>A: nothing to do,reduce msg num
    end
    opt if C_A//C_B
        B->>A: send [ clocks of C_B - C_A] and C_B
        A->>B: send [ clocks of C_A - C_B]
    end
    B->>+other-peers: if C_A//C_B,then broadcast C_B
    other-peers-)-B: similar to A and B
    
    other-peers->>+B: if D is init setup, req clocks by needs from peers

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• All message types:
  • ServerMsg:
    • EventTrigger
    • DiffReq
    • DiffRsp
    • ActiveSync
  • ClientMsg: only send latest clock
• Tips:
  • C_A refer to the latest clock of node A.
  • C_B : latest clock of node B.