InstantSend#

Overview#

Dash Core’s InstantSend feature provides a way to lock transaction inputs and enable secure, instantaneous transactions. The network automatically attempts to upgrade any qualifying transaction to InstantSend without a need for the sending wallet 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 ChainLock

    • Have at least the number confirmations (block depth) indicated by the table below

Network

Confirmations Required

Mainnet

6 Blocks (normal transactions)
100 Blocks (mining/masternode rewards)

Testnet / Regtest / Devnet

2 Blocks

The introduction of the Long-Living Masternode Quorum 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 minimized network congestion since only the isdlock message produced by the locking process is relayed to the entire Dash network. The lock message contains all the information necessary to verify a successful transaction lock.

Deterministic InstantSend#

Protocol version 70220 implemented deterministic InstantSend (see DIP22) which added the isdlock message as a replacement for the islock message. The islock message was deprecated and fully removed in protocol version 70231.

Management via Spork#

Spork 2 (SPORK_2_INSTANTSEND_ENABLED) is used to manage InstantSend. Spork 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 miner may still include any transaction, but blocks 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#

InstantSend Client

Direction

Peers

Description

tx message

→

Client sends InstantSend transaction

LLMQ Signing Sessions

Quorums internally process locking

Quorum(s) responsible for the transaction’s inputs lock the inputs via LLMQ signing sessions

Once all inputs are locked, the quorum responsible for the overall transaction creates the transaction lock (isdlock) via an LLMQ signing session

LLMQ Results

Quorum results broadcast to the network

←

inv message (isdlock)

Quorum responds with lock inventory

getdata message (isdlock)

→

Client requests lock message

←

isdlock message

Quorum responds with lock message

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