區塊鏈簡介
區塊鏈服務於虛擬貨幣，區塊鏈技術用個體自己算哈希數來進行貨幣發行，通過加密技術支持帳戶交易，通過分布式通信進行全節點賬本同步，提供架構來支持錢包等高級功能 。它的出現再次證明計算機和互聯網是強大工具，實體世界里的行業模型可以很好地在計算機世界里體現。
銳英源研究過區塊鏈平台多個源代碼版本，各個版本都進行了定制開發，客戶滿意，平台可靠穩定運行。這里分享2個方面的知識點：編譯和參數。
區塊鏈源代碼編譯
區塊鏈是開源的，一般也是用開源的操作系統，現在經常用ubuntu來當區塊鏈的運行平台。在ubuntu下正常的編譯步驟如下：
sudo apt-get update
sudo apt-get install build-essential libtool autotools-dev automake pkg-config libssl-dev libevent-dev bsdmainutils
sudo apt-get install libboost-all-dev
sudo apt-get install git
sudo apt-get install software-properties-common
sudo add-apt-repository ppa:bitcoin/bitcoin
sudo apt-get update
sudo apt-get install libdb4.8-dev libdb4.8++-dev
./autogen.sh
./configure
make
在ubuntu12下，這些步驟沒問題。但是到ubuntu14下，在處理libdb4.8行時，會提示找不到libdb，這時候不要慌，把libdb4.8去掉，變成如下行就可以：
sudo apt-get install libdb4.8++-dev
安裝源在識別時，不能用libdb4.8-dev來找到包，但是用后者就可以，后者也包含libdb4.8-dev，安裝后也可以編譯出來區塊鏈的可執行文件。這事件的原因就是開源的不全面性造成的，開源世界里遇到變化是常事。
另外要注意操作系統平台的32位或64位情況，一般是用64位平台操作系統才可以運行。
參數Configuring a blockchain
The parameters of a blockchain are configured after creating the chain by running multichain-util create [chain-name], and before starting the chain by running multichaind [chain-name].
Parameters are set in the params.dat file for each blockchain, which can be modified in any text editor. Once the blockchain is initialized, these parameters cannot be changed. To prevent accidental modification, a hash of the parameters is added to params.dat when the chain starts running. multichain-util create [chain-name]創建區塊鏈后，參數會配置上。
When new nodes attempt to connect to an existing blockchain, they first download a minimal set of blockchain parameters from the existing node, and write them to the params.dat file in the appropriate directory. Once they are granted permission to connect, they are able to download the full set of blockchain parameters.新節點想連接存在的區塊鏈，必須先下載已創建區塊鏈節點機器好的區塊鏈參數。
The parameters for a blockchain can be retrieved using the getblockchainparams API call. getblockchainparams 命令可以查看參數。
Full list of blockchain parameters
Below is a full list of parameters in the params.dat file, grouped by section.
Basic chain parameters
Parameter
Description
Example
chain-protocol
Use multichain for a MultiChain blockchain or bitcoin for a bitcoin-style blockchain with no permissions, native assets or streams.
multichain
chain-description
Textual description of the blockchain for display to users.
Internal chain
root-stream-name
Name of the root stream for general data storage (leave blank for none).
root
root-stream-open
Allow anyone with send permissions to write to the root stream.
true
chain-is-testnet
Whether to set testnet to true in the output of various JSON-RPC API calls. This is for compatibility with Bitcoin Core and does not affect any other testnet-like behavior.
false
target-block-time
Target average number of seconds between blocks, i.e. delay for confirming transactions. If this is below 10 seconds, it is recommended to set mining-turnover low, to minimize the number of forks.
60 (one minute)
maximum-block-size
Maximum number of bytes in each block, to prevent network flooding by a rogue miner.
1000000 (1MB)
Global permissions
Parameter
Description
Example
anyone-can-connect
Apply no restriction to connecting to the network, i.e. nodes do not require connect permissions.
false
anyone-can-send
Apply no restriction to sending transactions, i.e. signing transaction inputs.
false
anyone-can-receive
Apply no restriction to receiving transactions, i.e. appearing in transaction outputs.
false
anyone-can-receive-empty
Apply no restriction to addresses which appear in transaction outputs containing no native currency, assets or other metadata. Only relevant if anyone-can-receive=false. This allows addresses without receivepermission to include a change output in non-asset transactions, e.g. to publish to streams.
true
anyone-can-create
Apply no restriction to creating new streams.
false
anyone-can-issue
Apply no restriction to issuing (creating) new native assets.
false
anyone-can-mine
Apply no restriction to mining blocks for the chain, i.e. confirming transactions.
false
anyone-can-activate
Apply no restriction to changing connect, send and receive permissions of other users.
false
anyone-can-admin
Apply no restriction to changing all permissions of other users.
false
support-miner-precheck
Support advanced miner permission checks by caching the inputs spent by an administrator when setting admin or mine permissions – see permissions management for more information.
true
allow-p2sh-outputs
Allow pay to scripthash outputs, where the redeem script is only revealed when an output is spent. See permissions management for more information about permissions and P2SH addresses.
true
allow-multisig-outputs
Allow multisignature outputs, where more than one address is explicitly listed in a transaction output, and a given number of these addresses are required to sign in order to spend that output. See permissions management for more information about permissions and multisig outputs.
true
Consensus requirements
Parameter
Description
Example
setup-first-blocks
Length of initial setup phase in blocks. During the setup phase, the constraints specified by the other parameters in this section are not applied.塊里初始設置階段的長度。在設置階段，其它參數不生效。
1440
mining-diversity
Minimum proportion of permitted miners required to participate in round-robin mining to render a valid blockchain, between 0.0 (no constraint) and 1.0 (every permitter miner must participate). Unlike mining-turnover, this is a hard rule which determines whether a blockchain is valid or not.許可礦工最小比例，在循環挖礦來提出一個有效區塊鏈參與時需要
0.5
admin-consensus-admin
Proportion of permitted administrators who must agree to modify the admin privileges for an address, between 0 (no consensus required) and 1 (every admin must agree).
0.5
admin-consensus-activate
Proportion of permitted administrators who must agree to modify the activate privileges for an address, between 0 and 1.
0.5
admin-consensus-mine
Proportion of permitted administrators who must agree to modify mining privileges for an address, between 0 and 1.
0.5
admin-consensus-create
Proportion of permitted administrators who must agree to modify stream creation privileges for an address, between 0 and 1.
0.0
admin-consensus-issue
Proportion of permitted administrators who must agree to modify asset issuing privileges for an address, between 0 and 1.
0.0
Defaults for mining runtime parameters
lock-admin-mine-rounds
Ignore forks that reverse changes in admin or mine permissions after this many (integer) mining rounds have passed. A mining round is defined as mining-diversity multiplied by the number of permitted miners, rounded up. This prevents changes in the blockchain’s governance model from being reversed and can be overridden by each node using the lockadminminerounds runtime parameter.
10
mining-requires-peers
A node will only mine if it is connected to at least one other node. This is ignored during the setup phase or if only one address has mine permissions, and can be overridden by each node using the miningrequirespeers runtime parameter.
true
mine-empty-rounds
If there are no new transactions, stop mining after this many rounds of empty blocks. A mining round is defined as mining-diversity multiplied by the number of permitted miners, rounded up. This reduces disk usage in blockchains with periods of low activity. If negative, continue mining indefinitely. This is ignored during the setup phase or if target-adjust-freq>0, and can be overridden by each node using the mineemptyrounds runtime parameter.
2.5
mining-turnover
A value of 0.0 prefers pure round robin mining between an automatically-discovered subset of the permitted miners, with others stepping in only if a miner fails. In this case the number of active miners will be mining-diversity multiplied by the number of permitted miners, rounded up. A value of 1.0 prefers pure random mining between all permitted miners. Intermediate values set the balance between these two behaviors. Lower values reduce the number of forks, making the blockchain more efficient, but increase the level of mining concentration. Unlike mining-diversity, this is a recommendation rather than a consensus rule, and can be overridden by each node using the miningturnover runtime parameter.
0.5
Native blockchain currency
When creating a blockchain, a fundamental question is whether it should use a native currency (the equivalent of bitcoin as an asset). By default, MultiChain blockchains do not use a native currency. However you may wish to change this to create a market for transactions, whereby transactions bid for inclusion in a block by attaching transaction fees in the native currency, and miners are rewarded with these fees along with block rewards.
Parameter
Description
Example
initial-block-reward
Initial number of native currency units to award the miner of each block, in raw integer units.
0
first-block-reward
Use a different mining reward for the first block only, in raw integer units. Ignored if negative.
-1
reward-halving-interval
Each time this many blocks has passed, halve the per-block miner reward.
52560000
reward-spendable-delay
After a block reward is granted to a miner, the number of blocks until that reward can be spent.
1
minimum-per-output
Minimum quantity of native currency in every transaction output, in raw integer units.
0
maximum-per-output
Maximum quantity of native currency in every transaction output, in raw integer units.
0
minimum-relay-fee
Minimum native currency fee required in order to relay a transaction, in raw integer units. This can be overridden by the minrelaytxfee runtime parameter.
0
native-currency-multiple
How many raw integer units per display unit of the native currency, as used in the JSON-RPC API. For example in the bitcoin network this would be the number of satoshis per bitcoin.
100000000
Advanced mining parameters
Parameter
Description
Example
skip-pow-check
Skip checking whether block hashes demonstrate sufficient proof-of-work.
false
pow-minimum-bits
Minimum/initial proof-of-work difficulty, i.e. the number of leading zero bits in the block hash.
20
target-adjust-freq
Frequency of recalculating proof-of-work difficulty level, measured in seconds. For blockchains which don’t require proof-of-work, use a negative value to prevent recalculation.
86400 (1 day)
allow-min-difficulty-blocks
Ignore the current target difficulty level if blocks are taking too long to appear.
false
Transaction limits
Parameter
Description
Example
only-accept-std-txs
Only accept and relay transactions which qualify as ‘standard’, according to the criteria below.
true
max-std-tx-size
Maximum size of a standard transaction in bytes.
100000 (100k)
max-std-op-returns-count
Maximum number of OP_RETURN outputs (for general data) in standard transactions.
10
max-std-op-return-size
Maximum size of an OP_RETURN metadata output in a standard transaction, in bytes.
4096 (4K)
max-std-op-drops-count
Maximum number of inline OP_DROP metadata elements in a single output in standard transactions.
5
max-std-element-size
Maximum size of data elements in standard transactions, in bytes.
600
Advanced parameters
default-network-port
Default IP port to use for peer-to-peer communications between nodes (can be overridden by each node using the port runtime parameter).
8571
default-rpc-port
Default IP port to use for JSON-RPC calls to multichaind (can be overridden by each node using the rpcport runtime parameter).
8570
chain-name
Blockchain name, which is generally set by a call to multichain-util.
chain1
protocol-version
The version of the chain-protocol protocol used. This can be used to provide backwards compatibility with older versions of MultiChain – see creating a new blockchain.
10007
network-message-start
The four-byte “magic value” sent at the start of each peer-to-peer protocol message.
fddcc6f1
address-pubkeyhash-version
address-scripthash-version
private-key-version
address-checksum-value
These control the formatting of regular addresses, pay-to-scripthash (multisig) addresses and exported private keys. For more information, see address and key format.
Production recommendations
Below is a list of parameters whose values are crucial for long-term production deployments of MultiChain 1.0. (We expect MultiChain 2.0, now in development, to enable many parameters to be changed by administrator consensus in a running blockchain.)
target-block-time
Consider where your validator nodes will be deployed geographically and the latency between those locations. Ensure this value is long enough to enable consensus to be maintained between those nodes at your peak expected throughput. Use pre-production testing to determine a safe value and then add a 50-100% margin of error. This parameter should be tested together with maximum-block-size since larger blocks take longer to propagate.
maximum-block-size
Ensure this is large enough for expected future growth. Use pre-production testing to determine the block sizes for a given workload. Note also that for any given transaction throughput, an increase in target-block-time requires a corresponding proportional increase in maximum-block-size.
anyone-can-mine
Set to false unless you are certain you want to use proof-of-work mining, in which case ensure that target-adjust-freqis a positive number.
anyone-can-admin
Set to false unless you are certain you want any user connected to the blockchain to be able to perform administrative actions, which is a highly unusual case.
support-miner-precheck
Set to true if your blockchain is open to the public, or any participant might be motivated to conduct a denial-of-service attack against the network. (Miner prechecks are performed by MultiChain 1.0 beta 2 or later.)
mining-diversity
Ensure this is above 0.5 to prevent a long-running network split leading to two blockchain forks that can both continue growing in the long term.
admin-consensus-admin
admin-consensus-mine
To prevent any possibility of a future conflict between administrators leading to a fork, set these above 0.5. This means there will always be a single clear majority for any governance changes to the chain.
target-adjust-freq
Set to -1 unless you want to use proof-of-work mining in your blockchain, otherwise block creation could become difficult and CPU intensive over time. There is no reason to use proof-of-work in a chain which has permissioned miners who are governed by mining diversity.
max-std-op-return-size
Ensure this is large enough to accommodate the largest piece of data you will ever embed in the blockchain (but note the hard limit of 64 MB). The max-std-tx-size and maximum-block-size should both be at least a few hundred bytes larger than this value.
protocol-version
Set to 10008 or later (assuming your chain-protocol is multichain) so that your blockchain will support upgrading to new protocols in future versions of MultiChain.