Dash Core's InstantSendInstantSend - InstantSend is a service that allows for near-instant transactions. Through this system, inputs can be locked to specific transactions and verified by consensus of the masternode network. feature provides a way to lock transaction inputsinputs - An input in a transaction which contains three fields: an outpoint, a signature script, and a sequence number. The outpoint references a previous output and the signature script allows spending it. and enable secure, instantaneous transactionstransactions - A transaction spending satoshis.. The networknetwork - The Dash P2P network which broadcasts transactions and blocks. automatically attempts to upgrade any qualifying transaction to InstantSend without a need for the sending walletwallet - Software that stores private keys and monitors the block chain (sometimes as a client of a server that does the processing) to allow users to spend and receive duffs. to explicitly request it.

• To qualify for InstantSend, each transaction input must meet at least one of the following criteria:
  • Be locked by InstantSend
  • Be in a block that has a ChainLockChainLock - ChainLocks are a feature enabling near instant consensus on the valid chain. ChainLocks use Long-Living Masternode Quroums to mitigate 51 percent attacks and reduce uncertainty when receiving funds.
  • Have at least the number confirmationsconfirmations - A score indicating the number of blocks on the best block chain that would need to be modified to remove or modify a particular transaction. A confirmed transaction has a confirmation score of one or higher. (block depth) indicated by the table below

The introduction of the Long-Living Masternode QuorumLong-Living Masternode Quorum - Long-Living Masternode Quorums (LLMQs) are a Dash innovation that enable masternodes to perform threshold signing of consensus-related messages (e.g. InstantSend transactions). LLMQs provide a more scalable, general use quorum system than the ephemeral ones used prior to Dash Core version 0.14. feature in Dash Core 0.14 provided a foundation to scale InstantSend. The transaction input locking process (and resulting network traffic) now occurs only within the quorum. This minimizes network congestion since only the islock message produced by the locking process is relayed to the entire Dash network. This message contains all the information necessary to verify a successful transaction lock.

Management via Spork

Spork 2 (SPORK_2_INSTANTSEND_ENABLED) is used to manage InstantSend. SporkSpork - A spork is a mechanism unique to Dash used to safely deploy new features to the network through network-level variables to avoid the risk of unintended network forking during upgrades. 2 enables or disables the entire InstantSend feature. As of Dash Core 0.17.0, it also can be used to limit locking to transactions found in blocks.

In the event of a sustained overload of InstantSend, the spork can be set to a value of 1. This mode enables a clean transition to fully disabling InstantSend without interfering with ChainLocks. In this mode masternodes will stop creating locks for new transactions when they enter the mempool and will only lock them once mined into a block. Once all existing locked transactions are mined into blocks, InstantSend can then be disabled by setting the spork value to 0 without disrupting ChainLocks.

Mining Considerations

Note: A transaction will not be included in the block template (from the getblocktemplate RPC) unless it:

1. Has been locked, or
2. Has been in the mempool for >=10 minutes (WAIT_FOR_ISLOCK_TIMEOUT)

A minerminer - Mining is the act of creating valid Dash blocks, which requires demonstrating proof of work, and miners are devices that mine or people who own those devices. may still include any transaction, but blocksblocks - One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain. containing only locked transactions (or ones older than the timeout) should achieve a ChainLock faster. This is desirable to miners since it prevents any blockchain reorganizations that might orphan their block.

InstantSend Data Flow

Once a transaction lock is approved, the instantlock field of various RPCs is set to true (e.g. the getmempoolentry RPC).