P2Pool

Visualization of the P2Pool share chain

P2Pool is a decentralized Bitcoin mining pool that works by creating a peer-to-peer network of miner nodes.

Decentralized payout pooling solves the problem of centralized mining pools degrading the decentralization of Bitcoin, avoids the risk of hard to detect theft by pool operators, and has better fundamental resistance to DoS attacks than centralized pools.

Miners are configured to connect to a P2Pool node that can be run locally, alongside the miner. P2Pool users must run a full Bitcoin node which serves the purpose of independently validating transactions and the Bitcoin blockchain. P2Pool also supports merged mining and several alternative blockchains.

P2Pool 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, which can also result in a share if it meets P2Pool's difficulty.

Because of the importance of strengthening Bitcoin's decentralization some Bitcoin supporters donate to P2Pool miners, resulting in returns above 100% of the expected reward.

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 ten seconds, just as Bitcoin regulates it to generate one block every ten minutes.

Unlike Bitcoin, nodes do not know the entire chain - instead they only hold the last 8640 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 that 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 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 8640, whichever is smaller. Payouts are weighted based on the amount of work each share took to solve, which is 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. (A miner with the aim to harm others could withhold the block, thereby preventing anybody from getting paid. He can NOT redirect the payout to himself.) The remaining 99.5% 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.

Stales

P2Pool stales don't work the same way as stales on centralized pools. On a centralized pool a stale is work which is too old to be accepted by the pool's Bitcoin node; this kind of stale is very rare in P2Pool because each user runs their own local bitcoind.

On P2Pool stales refer to shares which can't make it into the sharechain. Because the sharechain is 60 times faster than the Bitcoin chain many stales are common and expected. However, because the payout is PPLNS only your stale rate relative to other nodes is relevant; the absolute rate is not.

There are two reported kinds of stales in P2Pool: "DEAD ON ARRIVAL" shares and orphan shares. Dead shares were too old by the time they arrived at your local P2Pool. Very high dead rates can indicate miner misconfiguration. Orphan shares are shares which were not extended by the rest of the P2Pool network, because some other miner's share was accepted first. Very high orphan rates may indicate network connectivity problems.

The P2Pool console output shows your relative stale rate compared to other P2Pool miners in the 'Own efficiency' column:

2012-01-07 20:57:51.797420 Pool stales: 13% Own: 13±2% Own efficiency: 100±2%

When you first start P2Pool claimed efficiency will be low and the error bounds on this estimate will be large, but as it runs the numbers will converge to their correct values.

If your efficiency is unusually low, make sure your network connection isn't overloaded, that your miners support long polling and are not set to work for excessive amounts of time, and that your bitcoind has multiple connections.

Joining the pool

Follow these steps to join the pool:

• Run Bitcoin with the RPC interface enabled: put rpcuser=USER, rpcpassword=LONG_RANDOM_SECRET_VALUE, and server=1 in bitcoin.conf (on separate lines)
  • Replace LONG_RANDOM_SECRET_VALUE with something long and random like the output of smashing your keyboard for a bit like fju4M78yAj3ds39pak92raK. You don't need to be able to remember it. If your RPC port becomes exposed to the internet a thief could steal your bitcoin if they could guess it, or use a brute force attack in order to find it.
  • Bitcoin 0.5 or later is required
  • It's important that your Bitcoin client be fully synchronized before starting. It's also better if you have the Bitcoin port forwarded
• Download p2pool:
  • Windows binary: See http://forum.bitcoin.org/index.php?topic=18313.0
  • Source download: https://github.com/forrestv/p2pool/tags
  • git: git clone git://github.com/forrestv/p2pool.git
• Run p2pool: (See below for additional options.)
  • Windows py2exe: run_p2pool.exe USER LONG_RANDOM_SECRET_VALUE
  • Source: python run_p2pool.py USER LONG_RANDOM_SECRET_VALUE
• 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
  • cgminer -O u:p -o http://127.0.0.1:9332/

Dependencies if running from source:

• Python 2.6 or higher
• python-argparse for Python 2.6 and lower
• Twisted (Ubuntu package python-twisted)

Miners

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

With all miners, using a HIGH FPS target (100?) or a LOW intensity (8 for cgminer?) helps a lot with reducing stales.

• cgminer works perfectly without any extra options. However, using multiple pools might cause problems, because long polling is only done for one pool.
• ufasoft works perfectly.
• DiabloMiner works fine after commit 3b731b9.
• Phoenix works fine after commit a658ef2.
• Poclbm works fine after commit 5e994e7.

P2Pool uses higher difficulty shares than most centralized pools, so you'll see fewer shares reported. This is normal and doesn't reduce your payments. It's also normal to see longpoll messages once per every ten seconds on average.

Useful features

• If upgrading P2Pool or changing its configuration, you can start another instance of P2Pool in parallel with the first. It will start normally, but realize that the worker and P2P listening ports are busy and keep trying to bind to them in the background. Thus, you can do almost-completely-seemless upgrades of P2Pool.
• If you run multiple P2Pool nodes or have trusted friends that run P2Pool, you can use -n to establish a constant extra P2P connection to them.

Option Reference

usage: run_p2pool.py [-h] [--version] [--net {bitcoin, litecoin}] [--testnet]
                     [--debug] [-a ADDRESS] [--logfile LOGFILE]
                     [--merged-url MERGED_URL]
                     [--merged-userpass MERGED_USERPASS]
                     [--give-author DONATION_PERCENTAGE] [--irc-announce]
                     [--p2pool-port PORT] [-n ADDR[:PORT]] [--disable-upnp]
                     [-w PORT] [-f FEE_PERCENTAGE]
                     [--bitcoind-address BITCOIND_ADDRESS]
                     [--bitcoind-rpc-port BITCOIND_RPC_PORT]
                     [--bitcoind-p2p-port BITCOIND_P2P_PORT]
                     [BITCOIND_RPCUSERPASS [BITCOIND_RPCUSERPASS ...]]

p2pool (version a7d3ae4)

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  --net {bitcoin, litecoin}
                        use specified network (default: bitcoin)
  --testnet             use the network's testnet
  --debug               enable debugging mode
  -a ADDRESS, --address ADDRESS
                        generate payouts to this address (default: <address
                        requested from bitcoind>)
  --logfile LOGFILE     log to this file (default: data/<NET>/log)
  --merged-url MERGED_URL
                        call getauxblock on this url to get work for merged
                        mining (example: http://127.0.0.1:10332/)
  --merged-userpass MERGED_USERPASS
                        use this user and password when requesting merged
                        mining work (example: ncuser:ncpass)
  --give-author DONATION_PERCENTAGE
                        donate this percentage of work to author of p2pool
                        (default: 0.5)
  --irc-announce        announce any blocks found on
                        irc://irc.freenode.net/#p2pool
  --disable-upnp        don't attempt to use UPnP to forward p2pool's P2P port
                        from the Internet to this computer

p2pool interface:
  --p2pool-port PORT    use port PORT to listen for connections (forward this
                        port from your router!) (default: bitcoin:9333,
                        litecoin:9338)
  -n ADDR[:PORT], --p2pool-node ADDR[:PORT]
                        connect to existing p2pool node at ADDR listening on
                        port PORT (defaults to default p2pool P2P port) in
                        addition to builtin addresses

worker interface:
  -w PORT, --worker-port PORT
                        listen on PORT for RPC connections from miners
                        (default: bitcoin:9332, litecoin:9327)
  -f FEE_PERCENTAGE, --fee FEE_PERCENTAGE
                        charge workers mining to their own bitcoin address (by
                        setting their miner's username to a bitcoin address)
                        this percentage fee to mine on your p2pool instance.
                        Amount displayed at http://127.0.0.1:WORKER_PORT/fee
                        (default: 0)

bitcoind interface:
  --bitcoind-address BITCOIND_ADDRESS
                        connect to this address (default: 127.0.0.1)
  --bitcoind-rpc-port BITCOIND_RPC_PORT
                        connect to JSON-RPC interface at this port (default:
                        bitcoin:8332, litecoin:9332 <read from bitcoin.conf if
                        password not provided>)
  --bitcoind-p2p-port BITCOIND_P2P_PORT
                        connect to P2P interface at this port (default:
                        bitcoin:8333, litecoin:9333 <read from bitcoin.conf if
                        password not provided>)
  BITCOIND_RPCUSERPASS  bitcoind RPC interface username, then password, space-
                        separated (only one being provided will cause the
                        username to default to being empty, and none will
                        cause P2Pool to read them from bitcoin.conf)

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)
• shares - broadcast message of the contents of shares - contains (shares)

History

This project was announced on June 17, 2011 by Forrest Voight.

The began testing against mainnet in mid-July, 2011. The pool was reviewed on a Bitcoin Miner post on July 26, 2011.

The software author's address for donations can be found in the signature section of his forum profile.

Donating to P2Pool miners

In order to encourage people to mine to P2Pool you can donate to the recent miners in proportion using a sendmany:

E.g. a bash script to donate 10 btc is:

~/src/bitcoin/src/bitcoind sendmany "" "$(GET http://forre.st:9332/patron_sendmany?total=10.0)"

You can replace "" with "accountname" if you want to pay from some specific bitcoind account, and you can replace forre.st with 127.0.0.1 if you're running a P2Pool node locally, so you don't have to trust that the URL gives accurate figures.

If you decide to donate you should announce it on the forums so that your donations provide the most incentive possible.

See Also

• Comparison of mining pools
• Pooled Mining

External Links

• P2Pool forum
• p2pool project on GitHub
• IRC Web #p2pool discussion and support