P2Pool

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P2Pool is a decentralized pool that works by creating a P2P network of miner nodes.

These nodes work on a chain of shares similar to Bitcoin's blockchain. Each node works on a block that includes payouts to the previous shares' owners and the node itself. There is no central point of failure, making it DoS resistant.

Overview

P2Pool shares form a "sharechain" with each share referencing the previous share's hash. Each share contains a standard Bitcoin block header, some P2Pool-specific data that is used to compute the generation transaction (total subsidy, payout script of this share, a nonce, the previous share's hash, and the current target for shares), and a merkle branch linking that generation transaction to the block header's merkle hash.

The chain continuously regulates its target to keep generation around one share every five seconds.

Unlike Bitcoin, nodes do not know the entire chain - instead they only hold the last 17280 shares (the last day's worth). In order to prevent an attacker from working on a chain in secret and then releasing it, overriding the existing chain, chains are judged by how much work they have since a point in the past. To ascertain that the work has been done since that point, nodes look at the Bitcoin blocks the shares reference, establishing a provable timestamp. (If a share points to a block, it was definitely made after that block was made.)

Payout logic

Each share contains a generation transaction that pays out to the previous n shares, where n is the number of shares whose total work is equal to 3 times the average work required to solve a block, or 17280, whichever is smaller. Payouts are weighted based on the amount of work each share took to solve - proportional to the p2pool difficulty at that time.

The block reward (currently 50BTC) and the transaction fees are combined and apportioned according to these rules:

A subsidy of 0.5% is sent to the node that solved the block in order to discourage not sharing solutions that qualify as a block. (An evil miner could withhold the block, thereby preventing anybody from getting paid. He can NOT redirect the payout to himself.) In addition, a subsidy of 0.5% is kept as a fee. The remaining 99% is distributed evenly to miners based on work done recently.

In the event that a share qualifies as a block, this generation transaction is exposed to the Bitcoin network and takes effect, transferring each node its payout.

Joining the pool

Follow these steps to join the pool:

  • Run bitcoin with the RPC interface enabled: put rpcuser=USER, rpcpassword=PASS, and server=1 in bitcoin.conf
  • Download p2pool:
  • Run p2pool: (See below for additional options.)
    • Windows py2exe: run_p2pool.exe USER PASS
    • git: python run_p2pool.py USER PASS
  • Run a miner daemon with long polling connecting to 127.0.0.1 (or the IP of the host running p2pool if you're mining remotely) on port 9332 with any username and password

Miners

This is all for the latest p2pool version, it includes several new workarounds.

Works as-is

cgminer (with the latest p2pool) works perfectly. A workaround was needed to get long polling to work, but it has no fixed long polling delay.

ufasoft, as far as I can tell by looking at the source but not actually running it (I couldn't get it to compile) should work perfectly too.

Needs patch to reduce stales

DiabloMiner has a bug where it waits half a second after receiving a long polling response. There is a 20% chance that a p2pool share will be generated in that window, resulting in all hashing until the next getwork being useless.

I have created a fork of DiabloMiner on GitHub that fixes this: https://github.com/forrestv/DiabloMiner Make sure to get the fast_long_polling branch! 

git clone git://github.com/forrestv/DiabloMiner.git
cd DiabloMiner
git checkout fast_long_polling

Built with JAR and Windows binary: http://u.forre.st/u/xsvenrwa/DiabloMiner_2e73cc.zip

Poclbm has a similar bug, but it waits a full second. GitHub fork: https://github.com/forrestv/poclbm Pull request: https://github.com/m0mchil/poclbm/pull/41 

git clone git://github.com/forrestv/poclbm.git
cd poclbm
git checkout fast_long_polling

No binary as of yet.

Phoenix has a similar bug (waiting a full second). Patch against SVN r112: http://im.forre.st/pb/74595264.txt

Not-compatible

puddinpop's RPC Miners don't have long polling and so will not work at all.

Option Reference

usage: run_p2pool.py [-h] [--version] [--testnet] [--debug] [-a ADDRESS]
                     [--p2pool-port PORT] [-n ADDR[:PORT]] [-l] [-w PORT]
                     [--bitcoind-address BITCOIND_ADDRESS]
                     [--bitcoind-rpc-port BITCOIND_RPC_PORT]
                     [--bitcoind-p2p-port BITCOIND_P2P_PORT]
                     BITCOIND_RPC_USERNAME BITCOIND_RPC_PASSWORD

p2pool (version a07e25c18d122565793536945c8cc65049eb1cce)

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  --testnet             use the testnet
  --debug               debugging mode
  -a ADDRESS, --address ADDRESS
                        generate to this address (defaults to requesting one
                        from bitcoind)
  -l, --low-bandwidth   trade lower bandwidth usage for higher latency
                        (reduced efficiency)

p2pool interface:
  --p2pool-port PORT    use TCP port PORT to listen for connections (default:
                        9333 normally, 19333 for testnet) (forward this port
                        from your router!)
  -n ADDR[:PORT], --p2pool-node ADDR[:PORT]
                        connect to existing p2pool node at ADDR listening on
                        TCP port PORT (defaults to 9333 normally, 19333 for
                        testnet), in addition to builtin addresses

worker interface:
  -w PORT, --worker-port PORT
                        listen on PORT for RPC connections from miners asking
                        for work and providing responses (default: 9332)

bitcoind interface:
  --bitcoind-address BITCOIND_ADDRESS
                        connect to a bitcoind at this address (default:
                        127.0.0.1)
  --bitcoind-rpc-port BITCOIND_RPC_PORT
                        connect to a bitcoind at this port over the RPC
                        interface - used to get the current highest block via
                        getwork (default: 8332)
  --bitcoind-p2p-port BITCOIND_P2P_PORT
                        connect to a bitcoind at this port over the p2p
                        interface - used to submit blocks and get the pubkey
                        to generate to via an IP transaction (default: 8333
                        normally. 18333 for testnet)
  BITCOIND_RPC_USERNAME
                        bitcoind RPC interface username
  BITCOIND_RPC_PASSWORD
                        bitcoind RPC interface password

Protocol description

P2Pool's protocol mirrors Bitcoin's P2P protocol in many ways. It uses the same framing (prefix, command, length, checksum, payload) and similar commands:

  • version - sent to establish a connection - contains (version, services, addr_to, addr_from, nonce, sub_version, mode, best_share_hash)
  • setmode - sent to update the mode sent in the version message - contains (mode)
  • ping - sent to keep connection alive - contains ()
  • addrme - request that the receiving node send out an addr for the sending node - contains (port)
  • addrs - broadcast list of nodes' addresses - contains (addrs)
  • getaddrs - request that the receiving node send count addrs - contains (count)
  • getshares - request that the receiving node send the shares referenced by hashes and parents of their parents, stopping at any share referenced by stops - contains (hashes, parents, stops)
  • share0s - broadcast message of the hashes of shares - contains (hashes)
  • share1as - broadcast message of the contents of shares that do not qualify as bitcoin blocks - contains (share1as)
  • share1bs - broadcast message of the contents of shares that qualify as bitcoin blocks - contains (share1bs)

The mode is 0 for low-bandwidth mode, which sends the hash of a share first before sending the entire share, or 1 for low-latency (default) mode, which forwards the entire (~170 byte) share always. The two nodes on either side of a connection use the minimum of their two preferences for that connection.

Reward distribution

  • Proportional, 0.5% fee. Transaction fees shared.


See Also

  1. [#p2pool channel on freenode to keep up with the

External Links

References

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