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Block Production Explained

For simplicity of the explanation let's consider the following notations:

  • r = producer_repetitions = 12 (hard-coded value)
  • m = max_block_cpu_usage (on-chain consensus value)
  • u = max_block_net_usage (on-chain consensus value)
  • t = block-time
  • e = produce-block-offset-ms (nodeos configuration)
  • w = block-time-interval = 500ms (hard-coded value)
  • a = produce-block-early-amount = w - (w - (e / r)) = e / r ms (how much to release each block of round early by)
  • l = produce-block-time = t - a
  • p = produce block time window = w - a (amount of wall clock time to produce a block)
  • c = billed_cpu_in_block = minimum(m, w - a)
  • n = network tcp/ip latency
  • h = block header validation time ms

Peer validation for similar hardware/version/config will be <= m

Let's consider the example of the following two BPs and their network topology as depicted in the below diagram

         +------+     +------+       +------+     +------+
      -->| BP-A |---->| BP-A |------>| BP-B |---->| BP-B |
         +------+     | Peer |       | Peer |     +------+
                      +------+       +------+

BP-A will send block at l and, BP-B needs block at time t or otherwise will drop it.

If BP-Ais producing 12 blocks as follows b(lock) at t(ime) 1, bt 1.5, bt 2, bt 2.5, bt 3, bt 3.5, bt 4, bt 4.5, bt 5, bt 5.5, bt 6, bt 6.5 then BP-B needs bt 6.5 by time 6.5 so it has .5 to produce bt 7.

Please notice that the time of bt 7 minus .5 equals the time of bt 6.5 therefore time t is the last block time of BP-A and when BP-B needs to start its first block.

A block is produced and sent when either it reaches m or u or p.

Starting in Leap 4.0 (a predecessor of Spring 1.0), blocks are propagated after block header validation. This means instead of BP-A Peer & BP-B Peer taking m time to validate and forward a block it only takes a small number of milliseconds to verify the block header and then forward the block.

Starting in Leap 5.0 (a predecessor of Spring 1.0), blocks in a round are started immediately after the completion of the previous block. Before 5.0, blocks were always started on w intervals and a node would "sleep" between blocks if needed. In 5.0, the "sleeps" are all moved to the end of the block production round.

Example 1: block arrives 110ms early​

  • Assuming zero network latency between all nodes.
  • Assuming blocks do not reach m and therefore take w - a time to produce.
  • Assume block completion including signing takes zero time.
  • BP-A has e = 120, n = 0ms, h = 5ms, a = 10ms
  • BP-A sends b1 at t1-10ms => BP-A-Peer processes h=5ms, sends at t-5ms => BP-B-Peer processes h=5ms, sends at t-0ms => arrives at BP-B at t.
  • BP-A starts b2 at t1-10ms, sends b2 at t2-20ms => BP-A-Peer processes h=5ms, sends at t2-15ms => BP-B-Peer processes h=5ms, sends at t2-10ms => arrives at BP-B at t2-10ms.
  • BP-A starts b3 at t2-20ms, ...
  • BP-A starts b12 at t11-110ms, sends b12 at t12-120ms => BP-A-Peer processes h=5ms, sends at t12-115ms => BP-B-Peer processes h=5ms, sends at t12-110ms => arrives at BP-B at t12-110ms

Example 2: block arrives 80ms early​

  • Assuming zero network latency between BP-A & BP-A Peer and between BP-B Peer & BP-B.
  • Assuming 150ms network latency between BP-A Peer & BP-B Peer.
  • Assuming blocks do not reach m and therefore take w - a time to produce.
  • Assume block completion including signing takes zero time.
  • BP-A has e = 240, n = 0ms/150ms, h = 5ms, a = 20ms
  • BP-A sends b1 at t1-20ms => BP-A-Peer processes h=5ms, sends at t-15ms =(150ms)> BP-B-Peer processes h=5ms, sends at t+140ms => arrives at BP-B at t+140ms.
  • BP-A starts b2 at t1-20ms, sends b2 at t2-40ms => BP-A-Peer processes h=5ms, sends at t2-35ms =(150ms)> BP-B-Peer processes h=5ms, sends at t2+120ms => arrives at BP-B at t2+120ms.
  • BP-A starts b3 at t2-40ms, ...
  • BP-A starts b12 at t11-220ms, sends b12 at t12-240ms => BP-A-Peer processes h=5ms, sends at t12-235ms =(150ms)> BP-B-Peer processes h=5ms, sends at t12-80ms => arrives at BP-B at t12-80ms

Example 3: block arrives 16ms late and is dropped​

  • Assuming zero network latency between BP-A & BP-A Peer and between BP-B Peer & BP-B.
  • Assuming 200ms network latency between BP-A Peer & BP-B Peer.
  • Assuming blocks do not reach m and therefore take w - a time to produce.
  • Assume block completion including signing takes zero time.
  • BP-A has e = 204, n = 0ms/200ms, h = 10ms, a = 17ms
  • BP-A sends b1 at t1-17ms => BP-A-Peer processes h=10ms, sends at t-7ms =(200ms)> BP-B-Peer processes h=10ms, sends at t+203ms => arrives at BP-B at t+203ms.
  • BP-A starts b2 at t1-17ms, sends b2 at t2-34ms => BP-A-Peer processes h=10ms, sends at t2-24ms =(200ms)> BP-B-Peer processes h=10ms, sends at t2+186ms => arrives at BP-B at t2+186ms.
  • BP-A starts b3 at t2-34ms, ...
  • BP-A starts b12 at t11-187ms, sends b12 at t12-204ms => BP-A-Peer processes h=10ms, sends at t12-194ms =(200ms)> BP-B-Peer processes h=10ms, sends at t12+16ms => arrives at BP-B at t12+16ms

Example 4: full blocks are produced early​

  • Assuming zero network latency between BP-A & BP-A Peer and between BP-B Peer & BP-B.
  • Assuming 200ms network latency between BP-A Peer & BP-B Peer.
  • Assume all blocks are full as there are enough queued up unapplied transactions ready to fill all blocks.
  • Assume a block can be produced with 200ms worth of transactions in 225ms worth of time. There is overhead for producing the block.
  • BP-A has e = 120, m = 200ms, n = 0ms/200ms, h = 10ms, a = 10ms
  • BP-A sends b1 at t1-275s => BP-A-Peer processes h=10ms, sends at t-265ms =(200ms)> BP-B-Peer processes h=10ms, sends at t-55ms => arrives at BP-B at t-55ms.
  • BP-A starts b2 at t1-275ms, sends b2 at t2-550ms (t1-50ms) => BP-A-Peer processes h=10ms, sends at t2-540ms =(200ms)> BP-B-Peer processes h=10ms, sends at t2-330ms => arrives at BP-B at t2-330ms.
  • BP-A starts b3 at t2-550ms, ...
  • BP-A starts b12 at t11-3025ms, sends b12 at t12-3300ms => BP-A-Peer processes h=10ms, sends at t12-3290ms =(200ms)> BP-B-Peer processes h=10ms, sends at t12-3080ms => arrives at BP-B at t12-3080ms

Running wasm-runtime=eos-vm-jit eos-vm-oc-enable on relay node will reduce the validation time.